Minerals Chapter 5

Minerals naturally occurring; non living; solid that has a definite composition and structure 4000 different minerals naturally occurring- not made by man inorganic- not alive, never was alive, didn’t come from living materials definite structure- atoms arranged in repeating patterns definite composition- specific chemical formula barite (BaSO4) talc [Mg3Si4O10(OH)2]

2 Main Composition Groups silicates (largest group) -Si & -O non-silicates carbonates -CO3 oxides -O sulfides -S halides -Cl or -F sulfates -SO4 native elements not combined with any other atom

Crystal Systems Atoms arranged in repeating patterns Not all samples show flat sides and sharp edges, it depends on where and conditions of the sample when it formed Constrictive environment creates small crystals, or masses of interlocking crystals Not restrictive environment allows crystals to grow large

How Minerals Form Cooling of hot magma (hot melted rock) Liquids containing the mineral evaporates, leaving the mineral

6 Major Crystal Systems Cubic- (halite) Orthorhombic- (sulfur) Tetragonal Monoclinic- (gypsum) Hexagonal- (quartz) Triclinic why 6? Lengths of the axis and the angles at which the axis intersect determines the crystal system

Physical Properties Unique properties or descriptions that help to identify minerals Hardness Luster Color Streak Cleavage vs. Fracture Specific Gravity Special properties

Hardness How easily a mineral can be scratched Mohs Hardness Scale-------------------Tools talc gypsum 2.5 fingernail* calcite 3.5 copper penny* fluorite 4.5 iron nail apatite 5.5 glass plate* feldspar 6.5 steel file quartz 7.0 streak plate* topaz corundum * tools we will use in lab. diamond to determine a mineral’s hardness A higher number mineral will scratch a lower number mineral

Luster How light is reflected from a mineral metallic—shines like a metal nonmetallic—does not shine like a metal can be dull, pearly, glassy, silky, brilliant

Color Look at mineral to recognize the color Usually a bad way to identify minerals, because most minerals can be different colors sulfur, olivine, orthoclase, malechite, copper

Streak the color of the mineral in powder form Use streak plate for minerals with hardness less than 7!

Cleavage Tendency for a mineral to break along smooth flat surfaces Why? Orderly arrangement of atoms causes a weakness where bonds aren’t as strong. Relates chemical makeup and chemical structure Cleavage is expressed in number of directions of cleavage & the angles at which they intersect

Directions of Cleavage 1 direction—sheets of paper 2 directions—a box with open top and bottom 3 directions—a brick Can have more than three, but it is difficult to see except in a fluorite octahedral

Angles of Cleavage Angles between the directions of cleavage are either 90o or NOT 90o Also described as perfect (easy to see) or poor (hard to see)

Fracture curved, broken of jagged edges without flat surfaces special type of fracture—conchoidal fracture looks like a shell with curved pattern seen in quartz

Specific Gravity Mass per unit of volume compared to H2O (density of mineral compared to the density of water) It is heavy for it’s size??

Special Properties Optical properties- transparent or translucent double refraction of calcite  Reaction to acid- members of the carbonate group fizz when put into acid…CO2 gas bubbles ex. calcite, malachite  Magnetism- some minerals are magnetic, others are attracted to a magnet ex. magnetite Taste ex. halite is “salty”

Special Properties Iridescence- rainbow colors like soap bubbles ex. Labradorite Chatoyancy- cat’s eye effect Asterism- six sided star appears in the mineral Phosphorescence or fluorescence- how minerals behave in ultraviolet light. Some change colors, some glow in the dark