Kristal-MineralGS1126 - 2 SKS teori

by:

Dr. hil. gendoet hartono

Semester 1, 2014-2015

The 7 Crystal Systems

Crystal Systems (cont.)

5

Sistem Heksagonal

• Terdiri dari 4 buahsumbu kristal

• Sumbu c tegak lurus dgn sumbu yg lain

a1, a2, a3 c

• a1 a2, a2 a3, a1 a3 = 120°

Cara menggambar:

Ð a+ / b¯ = 170

Ð b+ / d¯ = 390

b : d : c : = 3 : 1 : 6

Mineral Identification Basics

• HEXAGONAL CRYSTALS

HEXAGONAL - Three horizontal

axes meeting at angles of 120o and

one perpendicular axis.

a1

a2

a3

HEXAGONAL Crystal

Axes

c

Mineral Identification Basics• HEXAGONAL CRYSTALS

HEXAGONAL Crystal

Model

HEXAGONAL

This model represents a hexagonal

PRISM (the outside hexagon - six sided

shape). The top and bottom faces are

called PINACOIDS and are

perpendicular to the vertical “c” axis.

Within this model is the

SCALENOHEDRAL form. Each face is a

scalenohedron. Calcite often

crystallizes with this form.

Mineral Identification Basics• HEXAGONAL CRYSTALS

These hexagonal

CALCITE crystals

nicely show the six

sided prisms as

well as the basal

pinacoid.

Mineral Identification Basics• HEXAGONAL CRYSTALS

RHOMBOHEDRON

Dolomite

SCALENOHEDRON

Rhodochrosite

Quartz

Hanksite

Pyramid

Face

Prism

Faces

Prism

Faces

Pyramid

Faces

Vanadinite

Beberapa ahli

memasukkan sistem ini ke

dalam sistem heksagonal.

Demikian pula cara

penggambarannya juga

sama. Perbedaannya bila

pada trigonal setelah

terbentuk bidang dasar,

yang berbentuk segienam

kemudian dibuat segitiga

dengan menghubungkan

dua titik sudut yang

melewati satu titik

sudutnya.

Sistem Trigonal

Cara menggambar:

Sama dengan sistem

Hexagonal,

perbedaannya

hanya pada Sb c

bernilai 3.

Penarikan Sb a sama

dengan pada

Sistem Hexagonal.

Tourmaline

Mineral Identification Basics• TRIGONAL CRYSTALS

Quartz

Dolomite

16

Sistem Ortorombik

• Mempunyai sumbu kristal yang tegak lurus satu dgn yg lainnya

a bc

• Ketiganya mempunyai panjang yg berbeda a b c

Cara

menggambar:

Ð a- / b+ = 300

a : b : c = 1 : 4 : 6

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

ORTHORHOMBIC

Three mutually perpendicular axes of different

lengths.

ORTHORHMOBIC

Crystal Axes

ab

c

a

c

b

An Alternative Crystal

Axes Orientation

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

ORTHORHMOBIC

Crystal Model

ORTHORHOMBIC

This model shows the alternative

axes where the vertical “c” axis is

not the longest axis.

The model shows the outside

“brick” shape of the PRISM and the

inner shape is a DIPYRAMID. The

top and bottom faces are called

PINACOIDS and are perpendicular

to the “c” axis.

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

Topaz from Topaz

Mountain, Utah.

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

BARITE is also orthorhombic. The

view above is looking down the “c”

axis of the crystal.

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

STAUROLITE

Prism View

Pinacoid

View

Mineral Identification Basics• ORTHORHOMBIC CRYSTALS

This is a Staurolite TWIN

with garnets attached.

See u next week….