Identifying minerals Ch 5 section 2

Physical properties Color Streak Luster Cleavage/fracture Hardness Crystal shape density

Color- Enough said……. Established based on chemical composition in our crystalline structure- idiochromatic minerals. Ions of certain elements are highly absorptive of selected wavelengths of light. chromophores; elements which possess strong pigmenting capabilities. and copper (Cu) are chromophores. Sulfur- yellows Cobalt- blue Copper- orange Chromium- deep reds/purples/ yellows Iron- red/orange/brown Manganese- Not a reliable way (on it’s own) to identify minerals

Colored minerals Not a reliable way to identify minerals Due to the atoms in it’s crystalline structure Example- Chromium- purples, dark oranges, and reds Cobalt- deep blues Manganese- deep reds and purples Sulfur- bight yellows Color can also be hidden due to weathering of minerals

streak More reliable Tested as a result of the powder left behind after a mineral scratches on a streak plate Ceramic tile Metallic minerals generally leave behind a darker streak than non metallic minerals Not all minerals leave behind a streak (due to them being very hard) Streak is still not the best test

Luster- shiny-ness All minerals have some form of luster Metallic- looks like polished metal Non metallic- has a brilliant, pearly, glassy, or waxy luster Dull or earthy- looks like there is no luster at all

Cleavage breaks Nice neat geometric breaks Looks as through someone “cut” a piece out Mineral tends to break along a cleavage plane parallel to it’s weakness Spot of weakness in the mineral due to it’s structure

Fracture breaks Similar to a bone fracture- not a “clena break” but rough jagged pieces Minerals may look jagged, rough like sand paper, curved, or even sandy with little pieces crumbling off Uneven or irregular- broken wood or splinery fibrous fracture Conchodial- curves along broken parts

Hardness- Ability of a mineral to resist scratching based on what it can scratch Result of the minerals strong internal sturcture due to the attractive force between the minerals bonds Diamnonds has 4 strong bonds between C and O which is why it is the hardest mineral Not resistance to breaks (cleavage or fracture) Mohs hardness scale- compares minerals abilty to scratch one another based on 10 basic minerals

Crystal shape Minerals take on 6 basic shapes and are a result of the minerals environment such as pressure, temperature, climate, ect Isometric (cubic) Tetragonal Monoclinic Orthorombic Hexagonal Triclinic These are a result of a rotation about an axis (typically the y-axis) and unequal lengths

Density- specific gravity D=m/v Density- # of atoms in a crystal per amount of space the crystal takes up Heavier atoms typically leads to minerals with greater densities per given volume Triple beam balance, jelly balance, or liquid relationships are genrally the best ways to find density

Special properties- “glowing” Fluorescence- ability to reflect wavelengths of light at bright colors due to being exposed to UV light Calcite with the black light looked purple-blue Phosphorescence- minerals that keep reflecting wavelengths of bright colors even after the UV light is shut off

Special properties- appearance Chatoyancy- “silky” look where the mineral looks to have a soft silky surface Caused by fibers in the mineral Asterism- the mineral appears to have a star in the center when light is shown on it Sapphires Double refraction- bends light so that it looks like 2 images can be seen through the mineral (in crystal form) Looks like being cross eyed and the image may be bent like looking through a glass of water We passed around calcite

Special properties-energy Magetism- attraction to minerals that contain Fe in their crystalline structure React to the bar magnet Radioactivity- some minerals give off energy due to the instability with their atoms p+ and n+- in the nucleus U Ra- react to a Geiger counter