Crystal Interfacial Angles Even when the crystals are

Crystal Interfacial Angles • Even when the crystals are different sizes, angles between equivalent faces are the same • For different minerals, angles are different. 3 2 4 4 3 1 2 Quartz N. Lindsley-Griffin, 1999 1

Habit - distinctive shape of the way the mineral commonly (habitually) appears N. Lindsley-Griffin, 1999 Concentric shells -- malachite

Habit N. Lindsley-Griffin, 1998

Crystal shape and Habit result from internal atomic structure N. Lindsley-Griffin, 1998

Cleavage - tendency to break along planes of weak bonds N. Lindsley-Griffin, 1998

Mica cleaves along planes of the weakest bonds N. Lindsley-Griffin, 1998

Fracture describes how a mineral breaks on an irregular surface rather than along cleavage planes Types of fracture: Smooth Rough Splintery Conchoidal N. Lindsley-Griffin, 1998

Hardness -- the resistance to being scratched Mohs scale measures relative hardness, the ability of one mineral to scratch another Diamond Corundum Topaz Quartz Feldspar Apatite Fluorite Calcite Gypsum Talc 10 9 8 7 6 5 4 3 2 1 Steel file Glass (6. 5) (5. 5 - 6) Copper penny Fingernail (3. 0) (2. 5) Mohs hardness scale: 1 = softest mineral; 10 = hardest © Houghton Mifflin 1998; Lindsley 2000

The 10 minerals of Mohs relative hardness scale 3 Calcite 1 Talc 4 Fluorite 2 Gypsum 9 Corundum 6 Feldspar N. Lindsley-Griffin, 1999 5 Apatite 7 Quartz 8 Topaz 10 Diamond

Luster - the appearance of a mineral in reflected light Types of luster: Metallic Nonmetallic Pearly Vitreous Resinous Silky Dull Earthy Metallic luster of pyrite © Houghton Mifflin; N. Lindsley-Griffin, 1998. Earthy luster of limonite

Metallic Luster is characteristic of ore minerals and others that contain metal cations. N. Lindsley-Griffin, 1998

Resinous luster in sphalerite Pearly luster in talc N. Lindsley-Griffin, 1999