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Major building block of silicates
silicate tetrahedron SiO4-
Silicates combine to form minerals in two ways
1. Combine with cations (Na, K, Ca, Mg2+, Fa2+)
2. Can share oxygens with other Si-O tetrahedras
Types of silicate linkages:
- 1. Isolated tetrahedra
- 2. Single-chain linkages
- 3. Double-chain linkages
- 4. Sheet linkages
- 5. Frameworks/3D frameworks
- -Carbonate ions
- -Form sheets similar to sheet silicates
- -Seperated by layers of cations
- -O2- bonds with cations, usually metallic ions
- -ionically bonded minerals
- -S2- bonds with cations
- -almost all are opaque and metallic
- SO4 (2-) bonds with cations
-Occurs primarily as precipitate from briny water
Halogen anions (Cl-, Br-, F-, I-)
Form ionic bonds
Most have isometric crystal forms
What makes a gem? (4 characteristics)
-Beauty - as reflected by color and luster
- -Brilliance (enhanced by cutting and polishing)
- -Durability (based on hardness)
- -Rarity (and perceived rarity)
Quality and intensity of reflected light. Metallic vs. nonmetallic.
Not a reliable method for mineral ID. Useful to distinguish dark vs light colored minerals. Color changes are due impurities.
-The color of a mineral when it is powdered.
-Powdered mineral color is more reliable than the solid color of a mineral.
- -A measure of the minerals resistance to scratching and abrasion.
- -Function of crystal structure, types of bonds, types of atoms.
-Tendency of a mineral to break along flat, parallel surfaces
- -Breakage of a mineral not on planes of weakness.
- -Results in irregular shapes
- -Specific type: concoidal fracture - concentric disc-shaped fracture
-Geometric shape that a mineral develops when it grows in an unconfined space. Specific shape determined by its internal atomic arrangement.