Minerals Fracture Fracture is the tendency of a

Minerals

Fracture • Fracture is the tendency of a mineral to break along curved surfaces without a definite shape. These minerals do not have planes of weakness and break irregularly

Cleavage is the tendency of a mineral to break along smooth planes parallel to zones of weak bonding

Luster is a description of the way light interacts with the surface of a crystal. This is how you would tell someone how a mineral looks. It has nothing to do with color or shape, but is related to transparency , surface conditions, crystal habit and index of refraction. Vitreous Dull Adamantine - very gemmy crystals Dull - just a non-reflective surface of any kind Earthy - the look of dirt or dried mud Fibrous - the look of fibers Greasy - the look of grease Gumdrop - the look a sucked on hard candy Metallic - the look of metals Pearly - the look of a pearl Pitchy - the look of tar Resinous - the look of resins such as dried glue or chewing gum Silky - the look of silk, similar to fibrous but more compact Submetallic - a poor metallic luster, opaque but reflecting little light Vitreous - the most common luster, it simply means the look of glass Waxy - the look of wax Resinous Adamantine Metallic Silky

Streak • The streak of a mineral is the color it displays in finely powdered form. The streak maybe completely different from the color of the hand specimen. One of the simpliest ways of determining the strak of a mineral is to rub a specimen across a piece of unglazed porcelain known as a streak plate Magnetite – Black Streak Amphibole – grey/green streak Hematite – red/brown streak

Hardness • • • Hardness. Mineral. Test 1 Talc Fingernail (2. 5) 2 Gypsum 3 Calcite Copper coin (3) 4 Flourite. Knife blade (5. 5) 5 Apatite Glass plate (5. 5+) 6 K-feldspar 7 Quartz Streak plate (7) 8 Topaz 9 Corundum 10 Diamond

Vesicular texture Glassy texture Texture • Minerals may be rough, like sand, others may be smooth or chalky. Run your fingers on the rock. What does it feel like. rough & crystalline texture Pegmatitic Texture – big grains

Specific Gravity • Density or specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water. • Density = Weight/Volume

Crystal System Crystal shape can be helpful in identification. Most minerals have a crystalline structure and can form perfect crystals if allowed to grow in an unrestricted space. Crystal faces resemble cleavage faces because they are flat and reflect light as a single plane, but they are different from cleavage surfaces because crystals have complex geometric shapes. Perfect crystals are rare and are seldom encountered.

Crystal System 2 Isometric • • CRYSTAL SYSTEM - AXES LENGTHS - AXIAL ANGLES CUBIC All equal All 90 TETRAGONAL a=b not = c all 90 HEXAGONAL two are equal 2 are 90, one 120 ORTHORHOMBIC all unequal all are 90 MONOCLINIC all unequal two are 90 TRICLINIC all unequal none are 90 Monoclinic Hexagonal Tetragonal Orthorhombic Triclinic

Color Quartz Malachite Minerals have the same chemical composition but small variations of the quantity and distribution of some elements will give the same mineral different colors. Quartz Pyrite Quartz Olivine Quartz Limonite

• • • Mineral Rock Crystal Gem Ruby Diamond Sapphire Fossil Crystal System Specific Gravity Silicate Luster Streak Hardness Moh’s Scale Cleavage Fracture Ore Texture Emerald

Mini-Poster • • • Mineral Luster Crystal Gem Moh’s Scale Cleavage Fracture Fossil Crystal System Specific Gravity Silicate Streak Hardness Ore Texture