The building blocks of the Earth

Crystal Cave Chihuahua, Mexico
Contains some of the world’s largest natural crystals (up to 11 meters)
• translucent gypsum beams

any naturally occurring inorganic solid that possesses an orderly crystalline structure and can be represented by a chemical formula
1. Naturally occurring: Minerals form by natural, geologic processes
Rough diamond crystal in matrix
Diamond grown by chemical vapor deposition
2. Solid substance: Only crystalline substances solid
at temperatures encountered at Earth’s surface
Except Mercury which is naturally in liquid form
3. Orderly crystalline structure:
Crystals - regularly shaped objects due to orderly packing of atoms
Orderly arrangement of Na and Cl atoms in mineral Halite, and the non-mineral Obsidian
4. Generally inorganic
Sugar crystals are organic compounds (non-minerals)
Calcite (CaCO3 from marine organisms) crystals inside an Echinoderm fossil
5. Can be represented by a chemical formula
Composition - expressed by chemical formulas; vary within specific, well-defined limits

Quartz: Olivine
Silica (SiO2) (Mg,Fe) 2SiO4

an aggregate of minerals, pieces of preexisting rocks, or a mass of mineral-like matter

Luster: appearance or quality of light reflected from the surface of a mineral

•vitreous (glassy)
•dull or earthy (dull appearance)
•silky (like satin cloth)
•greasy (as though coated in oil)

Pearly Muscovite Vitreous Zircon Silky Satin spar
Earthy Limonite Greasy Opal

Tarnished (submetallic) and freshly-broken sample of Galena (metallic).

The Ability to Transmit Light (Diaphaneity)
•Opaque (no light is transmitted)
•Translucent (light is transmitted, but not an image)
•Transparent (both light and an image are visible through the sample)

Translucent Nephrite and Jadeite

Color: limited diagnostic property...