Geology Lab - Rock Identification

sedimentary rock

composed of pieces of other rocks or chemical properties produced by weathering and erosion of preexisting rocks

aphantic texture

crystals re formed but are too small to be seen with the naked eye ex. Felsite

fine-grained texture

crystals visible with the naked eye but are still very small ex. Rhyolite

metamorphic rock

produced by the alteration of preexisting rocks by heat, pressure, and fluids to such an extent that their original character is destroyed

mafic igneous rocks

pyroxene, amphibole, ca-plagioclase

Organic

sedimentary rocks formed from the carbon-rich relicts of organisms

Biochemical

sedimentary rocks with an organic texture of skeletal debris from organisms

igneous rock

solidify from hot molten material called magma (composed of silicates, oxides, gasses)

glassy texture

texture results from extremely rapid cooling, similar to ordinary glass ex. Obsidian

phaneritic texture

an igneous rock, individual rocks are large enough to see with the naked eye ex. Granite

Chemical

chemical sedimentary rocks are typically formed by precipitation dissolved minerals from concentrated solutions or evaporation of water

intermediate igneous rocks

intermediate plagioclase feldspars, pyroxenes, amphiboles and biotite

vesicular texture

open holes in igneous rocks formed by the preservation of bubbles in magma

felsic igneous rocks

orthoclase feldspare, muscovite, quartz

porphyritic texture

two distinct sizes of crystals, fine-grained and phenocrysts ex. Horneblende

Foliation

well-defined parallel alignment of constituent minerals or segregated into bands