Transcript Mineral - McEachern High School

Minerals of the Earth
What is a mineral?
• What objects in this classroom are considered minerals?
• Mineral: naturally occurring, inorganic solid with a specific
chemical composition and a definite crystalline structure.
• Minerals occur naturally and all minerals are inorganic (never
alive)
• All minerals are solids (definite shape and volume)
• The chemical composition of a mineral is unique to that
mineral and used for classification.
• Atoms arranged in geometric pattern Tetrahedral; gives the
crystalline structure of the mineral
• Well defined crystals= formed in open space
Minerals from Magma
• Magma: molten material found beneath the Earth’s surface
• Magma forced upward (density differences) where the
magma cools; compounds interact chemically to form
minerals
• Type and amount of elements found determine which
minerals will form
• Rate of cooling determines the size of mineral crystals
• Magma cools slowly: large crystals
• Magma cools quickly: small crystals form
Minerals from Solution
• Water in a solution can dissolve only so much of a solid before
the water becomes saturated.
• If solution becomes supersaturated (overfilled) with another
substance, mineral crystals begin to form
• Can also form when elements dissolve in supersaturated
solution
• Ex: Gypsum deposits form from evaporated water
Mineral Groups
• Silicates: minerals that contain silicon and oxygen, and usually
one or more other elements; 96% of minerals found in Earth’s
crust EX: feldspar and quartz (most common minerals);
unique structure accounts for the diversity of silicates
• Carbonates: minerals composed of one or more metallic
elements with the carbonate compound EX: calcite, dolomite,
and rhodochrosite; primary minerals found in rocks such as
limestone and marble; distinct colorations
• Oxides: compounds of oxygen and a metal; hematite and
magnetite are iron oxides (good source of iron); uraninite
valuable for source of uranium (generates nuclear power)
Mineral Identification
• Color: caused by trace elements or compounds; least
reliable clues to a minerals identity
• Luster: way a mineral reflects light from its surface;
either metallic (shiny surfaces) or nonmetallic (do not
shine like metals); caused by differences in chemical
composition
• Texture: how it feels to your touch; often used in
combination with other tests; smooth, rough, ragged,
greasy, soapy or glassy.
• Streak: the color of a mineral when it is broken up and
powdered; not always the same as the mineral color.
Rarely changes; cant be used to identify all minerals (if
harder than a porcelain plate)
Mineral Identification
• Hardness: most useful test; measure of how easily a
mineral can be scratched. Measured using Mohs scale of
hardness; determined by the arrangement of a mineral’s
atoms.
• Cleavage & Fracture: determined by atomic
arrangement; cleavage: mineral that splits relatively
easily along one or more planes. fracture: minerals that
break with rough or jagged edges and at random.
• Density & Specific Gravity: reflects the atomic weight
and structure of a mineral; useful identification tool;
sometimes too small to tell differences
Special Properties
• Double refraction: refraction of a single ray of light into two
rays creating two images (due to arrangement of atoms)
• Chemical composition: calcite fizzes when in contact with HCl;
releases CO2 in form of bubbling gas
• Special properties of specific minerals aid in identification
Gems
• These are valuable minerals that are prized for their rarity and
beauty
• Rubies, emeralds, and diamonds (rubies & emeralds more
valuable)
• Used for jewelry