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Rocks - Key tests
Question | Answer |
---|---|
Clay oxidation | Wacke/Greywacke |
Visible bedding planes | Siltstone Claystone |
Rounded pebbles | Sandstone Conglomerate Breccia |
Fizz test | Shale Phosphorite Dolomite |
Fizz test; fossils | Limestone |
Fizz test; plentiful fossils | Coquina |
Round, heavy | Concretions |
Oily smell; dusty; light heft | Coal |
Hardness: 7; organic nature; ooze origins | Chert |
Foliation; visible crystals; density | Shale Slate Quartzite Phyllite Marble Hornfels Greenstone Gneiss Argillite |
Green, greasy, streaky, and soft | Serpentine |
Foliated mica; garnets; density | Schist |
Crystalline, often salt-and-pepper | Amphibolite |
Contains large quartz or feldspar crystals | Porphyry |
Green; coarse | Peridotite |
Rare garnets; very coarse crystals | Pegmatite |
Often pinkish; exfoliation | Granite |
Dark with coarse grains | Gabbro |
Dark smears, unlike granite; often in dikes and sills | Diorite |
Soft, unless welded; angular clasts | Tuff |
Rusty, like cinders; numerous vesicles; heavier than pumice | Scoria |
Quartz crystals in fine-grained matrix | Rhyolite |
Floats; soft | Pumice |
Glassy luster, sharp edges, conchoidal fracture pattern | Obsidian |
Hornblende and plagioclase in fine-grained matrix | Dacite |
Fine grained, often with microscopic crystals only; can form dramatic columns | Basalt |
Fine grained with pyroxene and plagioclase | Andesite |