PHYSICAL GEOLOGY MINERAL IDENTIFICATION HELP SHEET
By Dr. George Hudak
| MINERAL NAME | DISTINGUISHING PROPERTIES |
| Quartz | Hexagonal crystals; Conchoidal Fracture; Hardness greater than glass (H=7 on Moh’s scale). |
| Plagioclase Feldspar | 2 cleavages at about 90°; Striations (twinning) present. |
| Potassium Feldspar | 2 cleavages at about 90°; Striations not present |
| Augite (pyroxene) | Usually dark green; 2 cleavages at about 90° (87°/93°) |
| Hornblende (amphibole) | Usually black or dark green; 2 cleavages at 60°/120° (56°/124°) |
| Olivine | Olive green color; Granular; Conchoidal fracture; Hardness greater than glass (H ~ 6.5 – 7). |
| Biotite | 1 perfect cleavage; Dark brown color. |
| Muscovite | 1 perfect cleavage; Colorless or silvery appearance. |
| Halite | 3 perfect cleavages at 90°; Tastes like salt (why, it is salt!). |
| Calcite | 3 perfect cleavages not at 90° (rhombohedral clvg); Fizzes readily when HCl acid applied. |
| Gypsum | Generally clear to white; One perfect cleavage, may show up to 3 cleavages; Easily scratched with a fingernail. |
| Magnetite | Metallic luster; Magnetic; Black streak. |
| Hematite | Metallic or non-metallic luster; Red-brown streak. |
| Galena | Metallic luster; 3 perfect cleavages at 90° |
| Pyrite | Hardness greater than glass (H ~ 6-6.5); Brassy yellow color; Metallic luster; Crystals commonly cubic; no cleavage. |
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