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 formulabarite (BaSO4)

talc [Mg3Si4O10(OH)2]

2 Main Composition Groups silicates

(largest group) -Si & -O

non-silicates carbonates -CO3

oxides -Osulfides -Shalides -Cl or -F

sulfates -SO4

native elements not combined with any other atom

Crystal SystemsAtoms 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 1. Cooling of hot magma (hot melted

rock)

2. Liquids containing the mineral evaporates, leaving the mineral

6 Major Crystal Systems 1. Cubic- (halite)

2. Orthorhombic- (sulfur)

3. Tetragonal

4. Monoclinic- (gypsum)

5. Hexagonal- (quartz)

6. 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

HardnessHow easily a mineral can be scratched

Mohs Hardness Scale-------------------Tools

1. talc2. gypsum 2.5 fingernail*3. calcite 3.5 copper penny*4. fluorite 4.5 iron nail5. apatite 5.5 glass plate*6. feldspar 6.5 steel file7. quartz 7.0 streak plate*8. topaz 9. corundum * tools we will use in lab. 10. diamond to determine a mineral’s

hardnessA 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

ColorLook 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

Streakthe 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 Cleavage1 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 CleavageAngles 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

Tasteex. 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