NATIVE ELEMENTS = UNSUR-UNSUR MURNI

Adalah unsur-unsur bebas, bukan merupakan unsur-unsur gabungan. Digolongkan menjadi tiga kelompok :

1. Logam / Metal, mineral-mineral yang tergolong dalam kelompo ini adalah

Mineral

(krauset.al 1959)

Mineral adalah suatu zat yang terdapat dalam alam dengan komposisi kimia yang khas dan biasanya mempunyai struktur kristal yang jelas, yang kadang-kadang dapat menjelma dalam bentuk geometris tertentu.Istilah mineral dapat mempunyai bermacam-macam makna; sukar untuk mendefinisikan mineral dan oleh karena itu kebanyakan orang mengatakan, bahwa mineral ialah satu frase yang terdapat dalam alam. Sebagaimana kita ketahui ada mineral yang berbentuk :

Lempeng Tiang Limas Kubus

Batu permata kalau ditelaah adalah merupakan campuran dari unsur-unsur mineral.Setiap mineral yang dapat membesar tanpa gangguan akan memperkembangkan bentuk kristalnya yang khas, yaitu suatu wajah lahiriah yang dihasilkan struktur kristalen (bentuk kristal). Ada mineral dalam keadaan Amorf, yang artinya tak mempunyai bangunan dan susunan kristal sendiri (mis kaca & opal). Tiap-tiap pengkristalan akan makin bagus hasilnya jika berlangsungnya proses itu makin tenang dan lambat.

[sunting] Kristal

Kristal adalah sebuah benda yang homogen, berbentuk sangat geometris dan atom-atomnya tersusun dalam sebuah kisi-kisi kristal,karena bangunan kisi-kisi kristal tersebut berbeda-beda maka sifatnya juga berlainan. Kristal dapat terbentuk dalam alam (mineral) atau di laboratorium. Kristal artinya mempunyai bentuk yang agak setangkup (symetris) dan yang pada banyak sisinya terbatas oleh bidang datar, sehingga memberi bangin yang tersendiri sifatnya kepada mineral yang bersangkutan.Benda padat yang terdiri dari atom-atom yang tersusun rapi dikatakan mempunyai struktur kristalen. Dalam suasana yang baik benda kristalen dapat mempunyai batas

bidang rata-rata & benda itu dinamakan kristal (HABLUR) & bidang rata itu disebut muka krsital.

Ada 32 macam gelas kristal yang dipersatukan dalam 6 sistem kristal, yaitu:

1. REGULER, Kubus atau ISOMETRIK ketiga poros sama panjang dan berpotongan tegak lurus satu sama lain (contoh : intan, pirit, garam batu)

2. TETRAGONAL (berbintang empat) ketiga poros tegak lurus satu sama lain, dua poros sama panjang sedangkan poros ketiga berbeda (contoh chalkopirit, rutil, zircon).

3. HEKSAGONAL (berbintang enam) Hablur ini mempunyai empat poros, tiga poros sama panjang dan terletak dalam satu bidang, bersilangdengan sudut 120 derajat (60 derajat), tetapi poros ke-empat tegak lurus atas bidang itu dan panjangnya berbeda (contoh apalit, beryl, korundum).

4. ORTOROMBIS (irisan wajik) ketiga poros tidak sama panjang du poros berpotongan siku-siku dan poros ketiga memotong miring bidang kedua poros tadi (berit, belerang, topaz)

5. MONOKLIN (miring sebelah) ketiga poros tidak sama panjang, dua dari porosnya berpotongan sorong & poros ketiga tegak lurus atas kedua poros tadi (gips, muskovit, augit)

6. TRIKLIN (miring, ketiga arah) ketiga poros tidak sama panjang dan berpotongan serong satu sama lain(albit, anortit, distin)

Bentuk kristal dibagi dalam 6 tata hablur yang didasarkan:

perbandingan panjang poros – poros hablur besarnya sudut persilangan poros – poros hablur

[sunting] Garis

kristal / mineral yang mempunyai kekerasan < 7 jika digosokkan pada lempengan porselin yang kasar biasanya meninggalkan ditempat penggosokan tsb suatu garis yang karakteristik dan seringkali berwarna lain dari mineral itu sendiri.

Pirit yang warnanya kuning emas meninggalkan garis hitam. Hematit (Fe2O3) yang berkilap kelogam – logaman atau memberigaris merah

darah Fluisvat memberikan garis putih (mineral yang berwarna terang tetapi memberi

garis putih)

[sunting] Skala Kekerasan MOH's

Kekerasan adalah sebuah sifat fisik lain, yang dipengaruhi oleh tata letak intern dari atom. Untuk mengukur kekerasan mineral dipakai Skala Kekerasan MOHS (1773-1839).

1. Talk, mudah digores dengan kuku ibu jari2. GIPS, mudah digores dengan kuku ibu jari3. Kalsit, mudah digores dengan pisau4. Fluorit, mudah digores dengan pisau5. Apatit, dapat dipotong dengan pisau (agak sukar)6. Ortoklas, dapat dicuwil tipis-tipis dengan pisau dibagian pinggir7. Kwarsa, dapat menggores kaca8. Topaz, dapat menggores kaca9. Korundum, dapat mengores topaz10. Intan, dapat menggores korundum

Bentuk Kristal Intan ialah benda padat besisi delapan (OKTAHEDRON)

1. K = 1 : Talk/Silikat magnesia yang mengandung air2. K = 2 : Gips (CaSO4), batu tahu3. K = 3 : Kalsit (CaCo3)4. K = 4 : Vluispat (CaF2)5. K = 5 : Apatit mengandung chloor6. K = 6 : Veldspat, kaca tingkap7. K = 7 : Kwarsa, pisau dari baja8. K = 8 : Topas; Silikat alumunium yang mengandung borium, batu permata9. K = 9 : Korsum (Al2O3 dalam corak merah, batu permata delima, corak biru batu

nilam/safir)10. K = 10 : intan batu permata

Masing-masing mineral tersebut diatas dapat menggores mineral lain yang bernomor lebih kecil dan dapat digores oleh mineral lain yang bernonor lebih besar. Dengan lain perkataan SKALA MOHS adalah Skala relative. Dari segi kekerasan mutlak skala ini masih dapat dipakai sampai yang ke 9, artinya no. 9 kira-kira 9 kali sekeras no. 1, tetapi bagi no. 10 adalah 42 kali sekeras no. 1

K.E. Kinge (1860) dalam Han Sam Kay mengelompokkan batu permata yang dijadikan perhiasan dalam lima belas kelas sebagai berikut :

1. Batu permata Kelas I, Nilai Keras antara 8 s/d 102. Batu Permata kelas II, Nilai Keras antara 7 s/d 83. Batu permata Kelas III

Batu permata kelas ini tergolong jenis batu mulia dan batu mulia tanggung, nilai kerasnya kira-kira 7, sebagian besar terdiri dari asam kersik (kiezelzuur), keculai pirus (tuquois)

4. Batu-Batu mulia Tanggung yaitu batu kelas IV, nilai keras antara 4 – 75. Batu kelas V

Batu kelas V nilai kerasnya dan kadar berat jenisnya sangat berbeda-beda. Warnanya gelap (kusam) dan kebanyakan agak keruh, tidak tembus cahaya, batunya sedikit mengkilap, dan harganyapun amat murah bila dibandingkan dengan harga batu mulia.

Dalam kelas ini termasuk batu marmer dan batu kelas V tidak tergolong batu mulia.

[sunting] Belahan

Belah adalah kecenderungan batu permata untuk membelah kearah tertentu menyusur permukaan bidang rata, lebih spesifik lagi ia menunjukkan kearah mana ikatan-ikatan diantara atom relative lemah dan biasanya reta-retak menunjukan arah belah.Belahan ialah sifat untuk menjadi belah menurut bidang yang agak sama licinnya

belahan baik sekali baik sedang buruk tidak ada belahan sama sekali

[sunting] Warna

Kenapa kita dapat melihat berbagai warna ?Warna dapat dilihat ketika terjadi beberapa proses pemindahan panjang gelombang, beberapa menyerap panjang gelombang spesifik dari spektrum yang dapat dilihat. Spektrum yang dapat dilihat terdiri dari warna merah, oranye, kuning, hijau, biru, nila dan violet.

Ketika terjadi pemindahan panjang gelombang akan mempengaruhi energi dan akan terjadi perubahan warna dan jika permata itu mengandung besi biasanya akan terlihat berwarna kelam, sedangkan yang mengandung alumunium biasanya terlihat berwarna cerah, tetapi juga ada mineral yang berwarna tetap seperti air (berkristal) dan dinamakan Idhiochromatic

Disini warna merupakan sifat pembawaan disebabkan karena ada sesuatu zat dalam permata sebagai biang warna (pigment agent) yang merupakan mineral-mineral yaitu : belerang warnanya kuning; malakit warnanya hijau; azurite warnanya biru; pirit warnanya kuning; magatit warnanya hitam; augit warnanya hijau; gutit warnanya kuning hingga coklat; hematite warnanya merah dsbnya.

Ada juga mineral yang mempunyai warna bermacam-macam dan diistilahkan allokhromatik, hal ini disebabkan kehadiran zat warna (pigmen), terkurungnya sesuatu benda (inclusion) atau kehadiran zat campuran (Impurities). Impurities adalah unsur-unsur yang antara lain terdiri dari Ti, V, Cr, Mn, Fe, Co, Ni, Cu, dan biasanya tidak hadir dalam campuran murni, unsur-unsur yang terkonsentrasi dalam batu permata rendah.

Aneka warna batu permata ini sangat mempersona manusia sehingga manusia memberi gelar “mulia” pada batu-batu itu, contoh intan yang hanya terdiri dari satu unsur mineral yakni zat arang merupakan benda yang padat yang bersisi delapan karena adanya zat

campuran yang berbeda akan menyebabkan warna yang berbeda : tidak berwarna, kuning, kuning muda, agak kebiru-biruan, merah, biru agak hijau, merah jambu, merah muda, agak kuning coklat, hitam yang dinamakan carbonado, hijau daun. Banyak mineral hanya memperlihatkam warna yang terang pada bagian-bagian yang tipis sekali. Mineral yang lebih besar dan tebal selalu memberi kesan yang hitam, tanda demikian antara lain diperlihatkan oleh banyak mineral.

Warna hijau muda; jika warna tersebut makin tua berarti makin bertambah Kadar Fe didalam molekulnya.

[The elements (which include over one hundred known minerals) are a diverse class when taken as a whole. Most of this diversity, however, is due to the diversity of the Non-metals Subclass. The Metals Subclass and related metal alloys contains metals whose properties are rather similar due to the common way in which they crystallize and bond. The greatest difference in the metals is color. The non-metals, however, are extremely diverse. For instance, the hardest mineral known to man is from this subclass, as well as one of the softest. The non-metals include some elements known as semi-metals who share some properties with metals but differ in other characteristics.

Metal alloys are minerals that are composed of combinations of different metals in one mineral. All native metals are impure usually by several percentage points, but these are not distinguished as distinct minerals unless they meet certain mineralogical criteria. Generally they must be consistent in their composition and have their respective elements occupy specific sites in their crystal lattice in order to be named as new minerals.

Alloys that are composed of semi-metals with metals are classified as sulfides but are sometimes listed as elements. They usually share similarities to other sulfides in their physical properties. These minerals are in the Selenides, the Tellurides, the Antimonides and the Arsenides Subclasses of the Sulfide Class. The main difference between elemental alloys and these semi-metal alloys is the presence of covalent bonding in these minerals as opposed to the strictly metallic bonding in pure metals and their metal alloys.

The most difficult to classify are the metal/non-metal mineral combinations. These minerals, which combine metals such as iron with the very non-metallic elements of carbon, nitrogen, phosphorous and silicon are quite unique and quite rare. They are not too different from sulfides which typically combine metals with sulfur. But the sulfides class is by convention limited to sulfur and semi-metal combinations as discussed above.

It might surprise people to find out that the Elements Class contains minerals that are composed of more than one element. Elements, by the chemical definition are composed of all the same atoms; whereas substances composed of two or more elements are compounds. The inconsistency is explained by allowing only those minerals whose bonding is similar to the more traditional elements. Metal alloys bond with metallic bonds and the carbon-carbon bond of diamond is similar to the carbon-silicon bond in

moissanite. This type of covalent bonding is called elemental bonds. All in all the Elements Class is a rather complicated and interesting class of minerals.

NATIVE COPPER Chemistry: Cu, Elemental Copper Class: Elements Group: Gold Uses: Minor ore of copper, ornamental stone Specimens

Native copper (copper found in a chemically uncombined state) has been mined for centuries and now is all but depleted as an economically viable ore. Other copper minerals are far more economical to mine and purify into metallic copper that is used for wiring, electrical components, pennies and other coins, tubing and many other applications. Native copper is still found in limited quantities in once-active mining regions. These finds are now valuable as minerological specimens and ornamental pieces. Fine specimens only rarely demonstrate crystal faces and these are prized above otherwise similar specimens.

PHYSICAL CHARACTERISTICS:

Color is copper colored with weathered specimens tarnished green. Luster is metallic. Transparency is opaque. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits include massive, wires and arborescent or branching forms as the

most common, whole individual crystals are extremely rare but when present are usually cubes and octahedrons. Occasionally, massive forms will show some recognizable crystal faces on outer surfaces.

Cleavage is absent. Fracture is jagged. Streak is reddish copper color. Hardness is 2.5-3 Specific Gravity is 8.9+ (above average for metallic) Associated Minerals are silver, calcite, malachite and other secondary copper

minerals. Other Characteristics: ductile, malleable and sectile, meaning it can be pounded

into other shapes, stretched into a wire and cut into slices. Notable Occurrences include Michigan and Arizona, USA; Germany; Russia

and Australia. Best Field Indicators are color, ductility and crystal habit.

THE MINERAL NATIVE GOLD Chemistry: Au, Elemental gold

Class: Elements Group: Gold Uses: Major ore of gold and as mineral specimens. Specimens

Gold is a pleasure to own and possess, as many people have discovered throughout the ages and around the world. Gold is a very stubborn element when it comes to reacting to or combining with other elements. Keeping this in mind, helps to explain many things about gold. There are very few true gold ores, besides native gold, because it forms a major part of only a few rare minerals, it is found as little more than a trace in a few others or it is alloyed to a small extent with other metals such as silver. Gold is almost indestructible and has been used and then reused for centuries to the extent that all gold of known existence is almost equal to all the gold that has ever been mined. Gold is a great medium metal for jewelry, as it never tarnishes. Native gold wires emerging from massive white quartz can make for a visually stunning specimen.

A few of the minerals that bear gold in their respective formulas are in a subclass of sulfides called the tellurides. The element gold seems to have an affinity for tellurium and this is one of the only elements that gold can bond with easily. In fact only a few rare tellurides are found with out gold. A few of the tellurides are nagyagite, calaverite, sylvanite and krennerite. These are all minor ores of gold but their contributions to the supply of gold pales next to native gold's own contribution. Occasionally these minerals are associated with native gold.

There are a number of minerals that are aptly named "Fool's Gold" because only a fool could believe they are gold! Actually it is easy for people who see shiny golden colored flakes sparkling at them from some rock they just picked up to believe that they have struck pay-dirt. Gold's ductility, sectility, density and softness are usually sufficient to distinguish it from the much cheaper imposters. The most famous "fool's gold" is the very common sulfide, pyrite. Chalcopyrite, marcasite and just about any golden colored sulfide has been also proven to be worthy the "fool's gold" moniker. Weathered flakes of biotite which can sport a bright yellow color and a nice flash of light when viewed just right, have also been mistaken for gold.

Gold specimens are sometimes artistically stunning and a good investment as well. After all, it is gold, which never seems to lose its value. Good natural specimens though are more expensive than their actual weight value. This is to be expected as good gold crystals are somewhat scarce (most are melted down for quick profits) and you really don't want a natural specimen to be worth what a lump of previously smelted and refined gold is worth, do you?.

PHYSICAL CHARACTERISTICS:

Color is golden "butter" yellow. Luster is metallic. Transparency is opaque. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits include massive nuggets and disseminated grains. Also wires,

dendritic and arborescent crystal clusters. Cleavage is absent. Fracture is jagged. Streak is golden yellow. Hardness is 2.5 - 3 Specific Gravity is 19.3+ (extremely heavy even for metallic minerals) Associated Minerals include quartz, nagyagite, calaverite, sylvanite,

krennerite, pyrite and other sulfides. Other Characteristics: ductile, malleable and sectile, meaning it can be pounded

into other shapes, stretched into a wire and cut into slices. Notable Occurrences include California and South Dakota, USA; Siberia,

Russia; South Africa; Canada and other localities around the world. Best Field Indicators are color, density, hardness, sectility, malleability and

ductility.

NATIVE SILVER Chemistry: Ag, Elemental silver Class: Elements Group: Gold Uses: Minor ore of silver for use in jewelry, coins and photographic films and

other industrial uses. Specimens

Silver has been mined for eons and has always been popular in jewelry and for coinage. Only in the past hundred years however, has the demand for silver been so great. The reason for this demand is the use of silver in the photography industry, which takes advantage of silver's reactivity to light. Native Silver is rare and much silver is produced from silver-bearing minerals such as prousite, pyrargyrite, galena, etc. Specimens of Native Silver usually consist of wires that are curved and intertwined together, making an inspiring mineralogical curiosity.

PHYSICAL CHARACTERISTICS:

Color is silver white with exposed specimens tarnishing black. Luster is metallic. Transparency is opaque. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits include massive and disseminated grains, wires and plates as the

most common, whole individual crystals are extremely rare but when present are

usually cubes, dodecahedrons and octahedrons. "Jack Frost" type crystal growth as shown on some specimens produces beautiful intricate structures. Wires can form coiled clusters that resemble rams horns.

Cleavage is absent. Fracture is jagged. Streak is silver white. Hardness is 2.5-3. Specific Gravity is variable according to purity 10-12 (well above average even

for metallic minerals) Associated Minerals are silver minerals such as acanthite and prousite,

cobaltite, copper, zeolites and quartz. Other Characteristics: ductile, malleable and sectile, meaning it can be pounded

into other shapes, stretched into a wire and cut into slices. Notable Occurrences include Michigan and Arizona, USA; Cobalt, Ontario;

Chile; and Germany. Best Field Indicators are color, tarnish, ductility and crystal habit.

NATIVE PLATINUM Chemistry: Pt, Elemental Platinum Class: Elements Group: Platinum Uses: Important ore of platinum and other rare metals. Platinum metal is

used for jewelry, chemical and other industrial uses as well as a currency stabilizer.

Specimens

Native platinum is an exotic mineral specimen and an expensive metal. Unfortunately, well formed crystals of platinum are very rare and the common habit of platinum is nuggets and grains. Pure platinum is unknown of in nature as it usually is alloyed with other metals such as iron, copper, gold, nickel, iridium, palladium, rhodium, ruthenium and osmium. The presence of these other metals tends to lower the density of platinum from a pure metal specific gravity of 21.5 to as low as 14 and very rarely any higher than 19 in natural specimens. Few of these rarer metals form significant deposits on their own and thus platinum becomes the primary ore of many of these metals. The presence of iron can lead to a slight magnetism in platinum nuggets and is a common enough property to be considered diagnostic.

The element platinum is extremely scarce in most crustal rocks, barely seen as even a trace element in chemical analysis of these rocks. However platinum seems to be much more concentrated in the mantle and can be enriched through magmatic segregation. Platinum's origin in the crust is from ultra-mafic igneous rocks and therefore platinum is associated with minerals common to these rocks such as chromite and olivine. Platinum's most common source however is from placer deposits.

Over the ages, the platinum became weathered out of the igneous rocks and were tumbled down streams and rivers where the extremely heavy grains and nuggets of platinum collect behind rocks and bends in the rivers and streams. These deposits, called placers, that form behind the rocks and bends are enriched in heavy grains as lighter material is carried further down stream. The heaviest grains are the nuggets of gold, platinum and/or other heavy minerals.

The metal platinum is a valuable metal that is gaining in importance. It is typically more expensive by weight than gold, mostly a product of its scarcity. Platinum is very non-reactive and for this reason it is used in chemical reactions as a catalyst. Metallic platinum can facilitate many chemical reactions without becoming altered in the process. It is also used in many anti-pollution devices, most notable is the catalytic converter, and has been given the nick name the "Environmental Metal". Native platinum is the primary ore of platinum, but deposits containing the rare platinum arsenide, sperrylite of the Pyrite Group, have made a huge contribution to the world's limited supply.

PHYSICAL CHARACTERISTICS:

Color is a white-gray to silver-gray, usually lighter than the platinum color of pure processed platinum.

Luster is metallic. Transparency is opaque. Crystal System: Isometric; 4/m bar 3 2/m Crystal Habits include nuggets, grains or flakes, rarely showing cubic forms. Cleavage is absent. Fracture is jagged. Hardness is 4 - 4.5 Specific Gravity is 14 - 19+, pure platinum is 21.5 (extremely heavy even for

metallic minerals). Streak is steel-gray. Other Characteristics: Does not tarnish, is sometimes weakly magnetic and is

ductile, malleable and sectile, meaning it can be pounded into other shapes, stretched into a wire and cut into slices.

Associated Minerals include chromite, olivine, enstatite, pyroxene, magnetite and occasionally gold.

Notable Occurrences includes Transvaal, South Africa; Ural Mountains, Russia; Columbia and Alaska, USA.

Best Field Indicators are color, density, weak magnetism, hardness, associations and ductility.

NATIVE MERCURY Chemistry: Hg, Elemental Mercury Class: Elements Group: Gold Uses: Minor ore of mercury, electrical switches, thermometers

Specimens

Mercury is unique, as it is the only metal that is liquid at room temperature, having a melting point of -40 C, and a boiling point of 357 C. This silvery liquid metal is very dense, yet has a high surface tension that causes is to form tiny little perfect spheres in the pores of the rocks it is found in. Many mineralogical characteristics simply do not apply to a liquid: there is no "hardness", since it cannot be scratched (nor can it scratch); there is no crystal structure, no fracture, no cleavage, no streak; all of course, at room temperatures. When frozen, mercury forms crystals in the rhombohedral system at low pressure, and in the tetragonal system at high pressure.

PHYSICAL CHARACTERISTICS:

Color is bright silvery metalic. Luster is metallic. Transparency is opaque. Crystal System does not apply Crystal Habits spherical droplets, or pools of mercury liquid. Cleavage does not apply Fracture does not apply Streak does not apply Hardness does not apply Specific Gravity is 13.5+ (very dense) Associated Minerals are cinnabar, calomel, and other secondary mercury

minerals. Other Characteristics: Mercury is a liquid! It also expans at a constant rate with

a rise in temperature. Notable Occurrences include Almaden, Spain; Idrija, former Yugoslavia; Italy;

California, Oregon, Texas, and Arkansas, USA. Best Field Indicators its a liquid!

IRON-NICKEL Chemistry: Fe-Ni, Elemental Iron-nickel Class: Elements Group: Iron Uses: as a mineral specimen and scientific studies. Specimens

Native Iron is quite often a misnomer as natural iron is not necessarily "native" to Earth since it rarely occurs on the Earth's surface by terrestrial processes. It is mostly found in the form of meteorites that have impacted the Earth's surface. A few rare terrestrial gabbros and sulfide deposits do contain elemental iron-nickel deposits, these are the only truly native iron-nickel. All natural iron, whether it is native or meteoritic, is actually an alloy of iron and nickel. The two elements are combined in varying

percentages from less than 6% nickel to as much as 75% nickel, although iron is by far more common than nickel.

The meteorites that contain iron-nickel crystals are facinating in their possible origins and diversity. It is postulated that another planet similar to Earth (a rocky planet) broke apart early in the formation of the solar system and is responsible for the iron-nickel debris that rains down upon the Earth on a daily basis. Since it is known that the Earth has a substantial amount of elemental iron and nickel in its core, this leads credence to this theory and gives us much to think about. Many, however, believe the meteor debris to be left over primordial material that the Earth and the other planets were built from.

Meteorites are very diverse and even novice collectors can distinguish samples from different known meteorites by their unique character. Often these meteorites have inclusions of large crystals of other minerals such as olivines or pyroxenes, etc or the iron has a unique crystal pattern that is characteristic.

Due to the nature of iron, care should be used in the preserving of valuable iron-nickel samples. Rust is iron's worst enemy and it is recommended to store iron samples with a dehydrating agent (dessicant).

PHYSICAL CHARACTERISTICS:

Coloris steel gray or black. Luster is metallic. Transparency is opaque. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits crystal form is extremely rare, when etched, meteoritic examples

may show interesting and complicated intergrowths of cystals according to different nickel-iron concentrates. Terrestrial samples are massive and appear as small flakes and irregular masses. Meteoritic samples are usually rounded, pitted and irregular.

Cleavage is absent but crystals will have distinct parallel partings. Fracture is hackly. Streak is gray metallic. Hardness is 4-5 Specific Gravity is 7.3-7.8 (heavy even for metallic) Other Characteristics: malleable, strongly attracted to magnets. Associated Minerals are olivine, pyroxenes, and some minerals that are only

found in meteorites. In terrestrial samples it is found with gold and platinum and with sulfide ores.

Notable Occurrences for meteoritic iron are best found in Antarctica, where meteorites are easy to spot against a background of snow and ice. Many specimens are found in Diablo Canyon, Arizona, USA; and in Gibbeon, Hoba, Namibia. Also Meteor Crater (Barringer Crater), Arizona, USA; Australia; Poland

and elsewhere. For terrestrial iron, good specimens can be found in the Kola Pennisula, Russia; Disco Island, Greenland; Kassel, Germany and New Zealand.

Best Field Indicators are color, malleability, attraction to magnets and forms.

THE MINERAL NATIVE ANTIMONY Chemistry: Sb, Elemental Antimony Class: Elements Group: Arsenic Uses: A very minor ore of antimony and as mineral specimens. Specimens

Antimony does not often form in its elemental state and is far more common in sulfides and sulfosalts such as stibnite, tetrahedrite, bournonite, boulangerite and jamesonite. It is also found in some oxides such as valentinite, stibiconite and senarmontite Due to the abundance of these antimony bearing ores and the rarity of native antimony, it is never an important ore of itself.

Native antimony is nearly indistinguishable from native arsenic. However the garlic odor which is sometimes found on arsenic specimens is not a characteristic of antimony and antimony does not tarnish as quickly or as severely as arsenic.

PHYSICAL CHARACTERISTICS:

Color is tin-white to a steel gray which can tarnish to darker grays. Luster is metallic but the tarnish will often dull the luster. Transparency: Crystals are opaque. Crystal System is trigonal; bar 3 2/m Crystal Habits include pseudocubic rhombohedral crystals. More commonly

found massive, botryoidal, lamellar and radiating. Cleavage is perfect in one direction (basal). Fracture is uneven. Hardness is 3 - 3.5 Specific Gravity is 6.6 - 6.7+ (heavy for a metallic mineral) Streak is tin-white to gray. Associated Minerals include sphalerite, stibnite and nickeline. Other Characteristics: Does not have a garlic odor. Notable Natural Occurrences include Chihuahua, Mexico; Wolfe Co., Quebec,

Canada and Kern Co., California, USA. Best Field Indicators are density, softness, color, crystal habits, lack of smell and

associations.

THE MINERAL NATIVE ARSENIC Chemistry: As, Elemental Arsenic Class: Elements

Group: Arsenic Uses: A very minor ore of arsenic and as mineral specimens. Specimens

Arsenic is historically the poison of choice for many murders, in reality and in fiction. Here, arsenic is dealt with only as mineral specimens and is not to be ingested. Although it has been used as a poison, arsenic has many chemical uses and is quite an important element.

Arsenic does not often form in its elemental state and is far more common in sulfides and sulfosalts such as arsenopyrite, orpiment, realgar, lollingite and tennantite. Due to the abundance of these arsenic bearing ores and the rarity of native arsenic, it is not an important ore of itself. Native arsenic is found in silver ore veins and is processed along with the silver ore and is therefore is a minor source of arsenic.

Native arsenic is usually found to have a trigonal symmetry but a very rare orthorhombic arsenic is known from Saxony, Germany and is named arsenolamprite. The two minerals are called polymorphs (many shapes) because they have the same chemistry, As, but different structures.

An obscure variety name for the concentrically banded or "shelly" arsenic is "scherbencobalt". Some arsenic will have some antimony in its structure and native antimony is nearly indistinguishable from arsenic.

PHYSICAL CHARACTERISTICS:

Color is tin-white which quickly tarnishes to dark gray or black. Luster is metallic but the tarnish will often dull the luster dramatically. Transparency: Crystals are opaque. Crystal System is trigonal; bar 3 2/m Crystal Habits include rare pseudocubic rhombohedral crystals and acicular

radial aggregates. More commonly found in fine grained masses with concentric bands or botryoidal crusts.

Cleavage is perfect in one direction (basal), but rarely visible. Fracture is uneven. Hardness is 3 - 4 Specific Gravity is 5.4 - 5.9+ (somewhat heavy for a metallic mineral) Streak is black. Associated Minerals include silver, dyscrasite, barite, cinnabar and nickeline. Other Characteristics: Will often have a garlic odor and is poisonous. Notable Natural Occurrences include Vosges, France; Kongsberg, Norway;

Saxony and Harz Mountains, Germany; Honshu, Japan; England; Italy and Santa Cruz Co., Arizona and New Jersey, USA.

Best Field Indicators are tarnish, density, softness, crystal habits, color, garlic smell and associations.

THE MINERAL BISMUTH Chemistry: Bi, Elemental bismuth Class: Elements Group: Arsenic Uses: An ore of bismuth and as mineral specimens. Specimens

Bismuth is rarely found in nature in its elemental form. Of growing interest in rock shops, however, are laboratory-grown bismuth crystals. These crystals, while not natural, are nonetheless very interesting to the mineral hobbyist and to others. The unique look that these clusters offer is really indescribable. Its color consisits of iridescent metallic yellow, blue and green hues.

Of interest to hobbyists are the pseudocubic "hopper" crystals that are always present on the laboratory produced specimens, they are not seen in but only the rarest of natural crystals. Hopper crystals are a unique crystallographic curiosity Just the edges extend outward from the center of the crystal leaving hollow stairstep faces between these edges. The hopper crystals form due to the disparity of growth rates between the crystal edges and the crystal faces.

PHYSICAL CHARACTERISTICS:

Color is silver white often with a multi-colored iridescent tarnish. Luster is metallic. Transparency: Crystals are opaque. Crystal System is trigonal; bar 3 2/m Crystal Habits include mostly massive foliated forms in natural specimens,

although there do exist some well formed natural crystals they are rather scarce. Laboratory grown crystals display trigonal hopper crystals that appear pseudocubic.

Cleavage is perfect in one direction (basal) Fracture is uneven or jagged. Hardness is 2 - 2.5 Specific Gravity is 9.7 - 9.8 (unusually heavy even for metallic minerals) Streak is silver to white. Other Characteristics: striations on cleavage surfaces. Associated Minerals include bismuthinite and ores of cobalt and silver found in

hydrothermal veins such as cobaltite and acanthite. Notable Natural Occurrences include Australia; San Baldomero and La Paz,

Bolivia; Devon, England; Germany and South Dakota, Colorado and California, USA.

Best Field Indicators are tarnish, density and cleavage. Hopper crystals in laboratory specimens are unmistakable.

NATIVE SULFUR Chemistry: S , Elemental Sulfur CLASS: Elements Uses: Major ore of sulfur which is used for chemical production Specimens

Sulfur, which is given a bad reputation because of its odor, can make a very beautiful mineral specimen, and fine quality examples are much sought after. The unmistakable deep yellow color is not matched by any other mineral and the nicely shaped crystal forms of sulfur add to its attractiveness. As for the odor, this occurs when water mixes with the sulfur and a small amount of hydrogen sulfide (H2S) gas is produced. Although only small amounts of H2S form from just moisture in the air, it is a powerful odor producer and is the dominating contributor to the odor of rotten eggs. Rest assured, though, that most specimens of sulfur, when kept dry, do not emit a strong odor and this is not difficult for collectors of fine sulfur specimens to ensure.

PHYSICAL CHARACTERISTICS:

Color is a strong yellow color in thick crystals and duller yellow in small crystals to pale yellow in massive or powdery forms. Can also be reddish or greenish yellow with impurities.

Luster is vitreous to more often resinous or earthy in massive forms. Transparency is transparent to translucent. Crystal System is orthorhombic; 2/m 2/m 2/m Crystal Habits include mostly massive or powdery forms but well shaped blocky

crystals are common. Crystals can be made up of two dipyramids, one with steeper faces than the other, prisms and/or pinacoids in various combinations.

Cleavage is very poor in two directions. Fracture is conchoidal. Streak is yellow. Hardness is 2. Specific Gravity is 2.0 - 2.1 (well below average) Associated Minerals are celestite, calcite, aragonite and gypsum. Other Characteristics: odor (see above), poor heat conductivity makes it brittle

when heated and can actually crack if held tightly in a person's hand. Notable Occurrences include Michigan and Ohio, USA; Sicily; Poland and

Chile. Best Field Indicators are color, odor, heat sensitivity, lack of good cleavage and

crystal habit.

THE MINERAL DIAMOND Chemistry: C, Elemental Carbon Class: Native Elements Subclass: Non-metallics

Group: Carbon Uses: usually as a gemstone and abrasive, also scientific uses. For natural diamond mineral specimens, see our diamond specimens page.

For Diamond Jewelry, see

Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.

As a gemstone, Diamond's single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of it's physical properties, diamond is the ultimate mineral in several ways:

Hardness: Diamond is a perfect "10", defining the top of the hardness scale. Clarity: Diamond is transparent over a larger range of wavelengths (from the

ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.

Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver!

Melting Point: Diamond has the highest melting point (3820 degrees Kelvin) Lattice Density: The atoms of Diamond are packed closer together than are the

atoms of any other substance

Diamond is a polymorph of the element carbon. Graphite is another polymorph. The two share the same chemistry, carbon, but have very different structures and properties. Diamond is hard, Graphite is soft (the "lead" of a pencil). Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system. Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

For natural diamond mineral specimens, see our diamond specimens page.For loose (cut) diamonds or diamond jewelry, see Abazias Diamonds.

PHYSICAL CHARACTERISTICS:

Color is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless.

Luster is adamantine to waxy. Transparency crystals are transparent to translucent in rough crystals. Crystal System is isometric; 4/m bar 3 2/m Crystal Habits include isometric forms such as cubes and octahedrons, twinning

is also seen. Hardness is 10 Specific Gravity is 3.5 (above average) Cleavage is perfect in 4 directions forming octahedrons. Fracture is conchoidal. Streak is white. Associated Minerals are limited to those found in kimberlite rock, an ultramafic

igneous rock composed mostly of olivine. Other Characteristics: refractive index is 2.4 ( very high), dispersion is 0.044,

fluorescent. Notable Occurrences include South Africa and other localities throughout

Africa, India, Brazil, Russia, Australia, and Arkansas. Best Field Indicator is extreme hardness.

GRAPHITE Chemistry: C, Elemental Carbon Class: Native Elements Subclass: Non-metallics Group: Carbon Uses: for the lead in pencils, as a toughener of steel, in high-strength

composites and as a lubricant. Specimens

Graphite is a polymorph of the element carbon. diamond is another polymorph. The two share the same chemistry, carbon, but have very different structures and very different properties.

Diamond is the hardest mineral known to man, Graphite is one of the softest. Diamond is an excellent electrical insulator, Graphite is a good conductor of

electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is usually transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the

hexagonal system.

Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

All of the differences between graphite and diamond are the result of the difference in their respective structures. Graphite has a sheet like structure where the atoms all lie in a plane and are only weakly bonded to the graphite sheets above and below. Diamond has a framework structure where the carbon atoms are bonded to other carbon atoms in three dimensions as opposed to two in graphite. The carbon-carbon bonds in both minerals are actually quite strong, but it is the application of those bonds that make the difference.

It may seem strange that one of the softest minerals (and a very slippery lubricant) is the high-strength component in composites used to build automobiles, aircraft, and of course golf club shafts.  It is the weakly bonded sheets that slide by each other to yield the slipperiness or softness.  Yet when those sheets are rolled up into fibers, and those fibers twisted into threads, the true strength of the bonds becomes apparent. The threads are molded into shape, and held in place by a binder (such as an epoxy resin). The resulting composites have some of the highest strength-to-weight ratios of any materials (excluding, of course, diamond crystals and carbon nanotubes).

Graphite can only be confused with the mineral molybdenite which is metallic bluish silver in color. However, molybdenite is much denser and has a silver blue streak.

Most graphite is produced through the metamorphism of organic material in rocks. Even coal is occasionally metamorphosed into graphite. Some graphite is found in igneous rocks and also as nodules inside of iron meteorites.

PHYSICAL CHARACTERISTICS:

Color is black silver. Luster is metallic to dull. Transparency crystals are opaque Crystal System is hexagonal; 6/m 2/m 2/m Crystal Habits include massive lamellar veins and earthy masses. also as scaly

granules in metamorphic rocks. Hardness is 1 - 2 Specific Gravity is 2.2 (well below average) Cleavage is perfect in one direction. Fracture is flaky. Streak is black gray to brownish gray. Associated Minerals include quartz, calcite, micas, iron meteorites and

tourmalines. Other Characteristics: thin flakes are flexible but inelastic, mineral can leave

black marks on hands and paper, weakly conducts electricity.

Notable Occurrences include New York and Texas, USA; Russia; Mexico; Greenland and India.

Best Field Indicator is softness, luster, density and streak.