Minerals. What is a mineral? Naturally occurring inorganic (no living thing or remains) Solid...
-
Upload
myron-hensley -
Category
Documents
-
view
258 -
download
1
Transcript of Minerals. What is a mineral? Naturally occurring inorganic (no living thing or remains) Solid...
What is a mineral?
• Naturally occurring• inorganic (no living thing or remains)• Solid• Definite shape ( arranged in an orderly
pattern)• definite chemical composition
Is it inorganic?
• Coal?• No, it is not a mineral- How is it made?• magnetite • Yes, a mineral• pearl• No, not a mineral- How is it made?
Does it occur naturally?
• Quartz• yes, a mineral- one of the last minerals to
form from a magma chamber.• Silver• yes, a mineral• steel• no, not a mineral- How is it made?
Solid in crystalline form?
• Petroleum• no, not a mineral- What is its natural form?• mercury• no, not a mineral- What is its natural form?• glass• not a mineral- What is its form? • amorphous
Definite chemical composition?
• Calcium• yes, Ca a mineral• Graphite• yes, C• Concrete• no, not a mineral- Why?
Rock forming minerals
• Over 3000 minerals• only 20 are common, these are rock
forming minerals• two main groups- silicates and nonsilicates
Silicates
• 96% of the crust• contain silicon (Si) and Oxygen (O)• Feldspars are the most common silicate
minerals, contain Ca, K, and Na• Examples- Orthoclase and plagioclase• Ferromagnesium- contain Fe and Mg
Nonsilicates• 4% of the crust• No silica• Six major groups• carbonates-ex. Calcite• halides- ex halite• native elements- Made of one element ex.
copper and silver• oxides- hematite and corundum• sulfates- gypsum• sulfides- galena, pyrite
Crystal Structure
• Specific geometric arrangement of atoms or ions
• Crystal = natural solid with a definite shape• Can be seen under microscope or with the
aid of x rays
Identifying Minerals• Characteristics of Minerals• Each mineral has specific properties that
provide useful clues for identifying minerals.
• Optical properties- properties will be identified by looking at the mineral.
• Tests- tools are used to run tests on the mineral.
Optical PropertiesColor
• Most easily observed• ex. Sulfur is bright yellow, azurite is deep
blue• least reliable characteristic
– quartz consists of many colors– weathering may hide true color
Luster• Light reflected from the surface of a mineral
• metallic luster- like polished metal like silver• All others are non metallic• vitreous luster- reflects like glass• pearly luster• adamantine- brilliant luster ex. Diamond or gems• other lusters include: waxy, greasy, dull, earthy
Crystal Shape• Regularly shaped particles, or pattern. • Most crystal shapes are hard to identify.• six crystal systems
– cubic ex. Halite, Pyrite– orthorhombic ex. Sulfur– tetragonal ex. Chalcopyrite– hexagonal ex. Plagioclase, Orthoclase– monoclinic ex. Micas– triclinic ex. Kyanite
Cleavage
• The tendency to split along certain flat surfaces and is related to types of bonds
• ex. Mica (general name) splits easily in one direction, it has one perfect cleavage ( splits in parallel sheets)
• Example- biotite and muscovite
Fracture• Some minerals do not break along cleavage
planes • instead they fracture or break unevenly into
curved or irregular pieces• splintery or fibrous fracture- looks like
pieces of broken wood• conchoidal- curved surfaces like the inside
of a shell
Simple TestsStreak Test
• The color of a mineral in powdered form• observed by rubbing the mineral against a
piece of unglazed ceramic tile called a streak plate
• the streak is not always the same color as the mineral
• mineral that have a hardness higher than the streak plate can not be tested
Hardness Test• The ability to resist scratching• hardness does not mean resistance to
cleavage or fracture• the hardness of an unknown mineral may be
determined by using Moh’s Hardness Scale• -this scale lists 10 minerals in order of
increasing hardness• -Softest is talc with a hardness of 1• The hardest is diamond with a hardness of
10
Moh’s Hardness Scale• Mineral hardness common test• talc 1 easily scratched by fingernail• gypsum 2 can be scratched by fingernail• calcite 3 can not scratch a copper penny• fluorite 4 can easily scratch a penny • Apatite 5 can barely scratch glass• Feldspar 6 can scratch glass • quartz 7 very easily/deeply scratches steel and glass• topaz 8 scratches quartz• corundum 9 no simple tests• diamond 10 scratches everything
Specific Gravity
• The ratio of the weight of the mineral to the weight of an equal volume of water.
• Each mineral has its own specific gravity• Can be used to identify a mineral
Acid Test
• Used to easily identify calcite
A drop of HCl dropped onto Calcite will cause it to effervesces. The bubbles are CO2 gas.
• Dolomite also responds to the acid test but not as violently and only in powdered form.
Special Properties• Magnetism- Can attach a magnet• Fluorescence- the ability to glow under
UV light ex. Calcite appears red under UV
• Phosphorescence- minerals that continue to glow after a UV light is removed.ex sphalerite
Special Properties con’t• Double refraction-
crystals that bend light in such a way that they produce a double image of any object viewed.
• Radioactivity- certain atoms have unstable electron or neutron arrangements. These minerals activate a Geiger counter.