Geology

• What is a mineral?

• What is a gem?

• What is a rock?

• How are these formed?

• Edited from WARDS Geometry of Crystals Lab

Mineral Criteria1. occurs naturally on Earth

Mining: Dig for Diamonds Park

2. is inorganically formed ( does not contain carbon) Exceptions are diamonds and graphite = pure carbon

Criteria continued

3. a solid at standard temp and pressure

4. Elements that make up the substance are combined in fixed proportions

5. The orderly arrangement of atoms that make up the substance produce a definite and repeating geometric pattern = characteristic crystal form

Minerals Is an element (ex. Gold, Au)

or a compound (ex. Quarts or

pyrite FeS2) found naturally in rocks and soils

There are more than 3500 minerals identified

New minerals are being found every year

Periodic Table

• 8 elements account for 98%of Earth’s crust

• These elements combine to form minerals

Oxygen Silicon Aluminum

Iron Calcium Sodium

Potassium Magnesium

Mineral Identification

• Based on physical and chemical traits

• Initially classified using one or more of the following physical properties

• 1. color 5. specific gravity

• 2. luster 6. cleavage or

• 3. hardness fracture

• 4. streak 7. crystal form

Color

• Least reliable trait

• Color can vary

• Color can change when exposed to moisture, high or low temperatures or weathering

Luster• Physical appearance

of the unweathered surface

• Way it reflects sunlight

• Metallic or nonmetallic (glassy, pearly, silky, greasy or brilliant)

Hardness• Is the resistance of a mineral’s smooth

surface (face) to being scratched by a point or an edge

• Mohs Hardness Scale has a range • 1 (soft, easily scratched – ex. Talc) to • 10 (hard – ex. Diamond)

• Any mineral can scratch a mineral with a lower hardness

• Tools for Testing Hardness• You typically do not carry around a

supply of the 10 minerals on the hardness scale. However, you can use the following items to help estimate the hardness of a mineral:

• Finger Nail (H = 2.5)• Penny (H = 3)• Knife Blade (H = 5.5)• http://zircon.mcli.dist.maricopa.edu/aaim/

linear/L1.html

Streak• Color of a mineral in its ground or powdered

form

• The powder is formed when the mineral is rubbed across an unglazed porcelain plate

• More reliable than color

• Plate has a hardness of 7 and is white

• Scratch test cannot be used on minerals of the same color or hardness

Specific Gravity (Relative Density)

• Specific gravity is the ratio of a mineral’s mass to the mass of an equal volume water.

• Very reliable

Cleavage or FractureCleavage: a break along a smooth, flat

plane producing smooth flat surfaces called faces

Ex. Galena

Fracture: a break that is not smooth but produces irregular surfaces

Ex. Quarts

Crystal Form• One of the most useful physical

characteristics

• Crystal forms result from the internal atomic arrangement of a mineral

• Repetition of these arrangements results in crystal systems which produce the visible shape of the mineral

Pyrite : “Fool’s Gold”

• FeS2

• Is the result of many atoms of iron and sulfur forming a crystalline solid with a definite internal arrangement

All crystals can be categorized into 1 of 6 crystal systems

• As defined by axes

• Axes are imaginary straight lines that pass through the center of the crystal faces at right angles to these faces and intersect at the center of a perfect crystal

Isometric or Cubic

Characteristics• 3 equal exes intersecting

at right angles to each other

• Same measure• 6 faces• Each face is a square• Angle between two

adjacent sides is 90o

• Ex. Galena, halite, pyrite

Hexagonal• Four axes • 3 of the 4 intersect at 60o

angles to others in the same plane

• 4th axis intersects the other 3 at a 90o angle

• Each of the similar 6 faces join each other at 60o

• 2 more identical faces are different form the other 6

• 2 identical faces form 90o with the other 6

• Ex. Calcite, quartz and apatite

Tetragonal• All 3 axis intersect at

90o

• 2 of the 3 axis are of equal length

• Four identical often rectangular faces and two square faces

• All adjacent faces hit at 90o

• Ex. Chalcopyrite, zircon

Orthorhombic• 3 axis intersect at 90o

• None of the axis are equal length

• Four of the faces form similar rectangles

• 2 of the other faces are similar rectangles but different from the first 4

• All adjacent sides meet at 90o

• Ex. Olivine, silfur, topaz

Monoclinic• 3 axes none of equal

length• Only 2 axes intersect at

90o

• 4 identical or similar faces• 2 identical faces unlike

the first 4• 6 sided prism• Faces meet at 90o and

other angles• Ex. Mica, gypsum,

orthoclase, hornblende

Triclinic

• 3 unequal axes• None of the axes

intersect at 90o

• Four similar or identical polygons and 2 larger similar or identical polygons different form the first 4

• None of the faces intersect at 90o

• Ex. feldspars

Gems

• A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which — when cut and polished — is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.

• http://en.wikipedia.org/wiki/Gemstone

Rocks (more info to come)

Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary and metamorphic. They are further classified according to particle size. The transformation of one rock type to another is described by the geological model called the rock cycle.

• http://en.wikipedia.org/wiki/Rock_(geology)

Mining

http://bldgblog.blogspot.com/2005/08/worlds-largest-diamond-mine.html