Primarily quartz, Random crystals, Large crystals feldspar, colors vary, mostly Granite muscovite, biotite from feldspars Intrusive Plagioclase, Same material as Large crystals hypersthene, basalt, slow to Gabbro olivine, augite cool Fine grained Plagioclase, – Dark grey to black, may be too fine to hypersthene, Basalt difficult to break see crystals olivine, augite Extrusive Fine grained, Usually light Primarily quartz, some scattered colored, may have Rhyolite feldspars large crystals gas bubbles Large gas Dark color, low Glass-like, Mineral bubbles, density, blown Scoria grains uncommon from volcanoes Volcanic - Extrusive Glass-like, cools Conchoidal too quick to form Black glass fracture; may have Obsidian crystals white crystals TYPE: SEDIMENTARY ROCKS Group Particle Size Composition Comments Rock Name Coarse grains, > Any rock type Rounded Conglomerate 2 mm (quartz common) fragments Color depends on Fine grains, Quartz with other other minerals, Sandstone Clastic < 2 mm mineral fragments sandpaper feel Formed from mud, Very fine grains, Quartz and clay has very thin but Shale too small to see particles visible layers Varies, but Carbonaceous From compacted, usually fine Lignite material non-marine plants grained Biological Fizzes with Fine grained Calcite Limestone vinegar Evaporate, pinkish Chemical Very fine grained gypsum Gypsum color TYPE: METAMORPHIC ROCKS Group Particle Size Composition Comments Rock Name Fine grained, From minerals Dense; thin minerals not with basal pieces; parent Slate visible cleavage: rock is shale Feldspar, quartz, Light & dark color Medium to coarse may have mica, bands, parent rock Gneiss Foliated grained iron minerals granite or diorite Varieties named Muscovite, biotite, Medium to coarse for major minerals; feldspar, quartz, Schist grained parent rock is tourmaline, others phyllite Visible, medium to Parent rock is Calcite (CaCO3) Marble coarse grains limestone Fine grained, Clay minerals, Dense, dark color, Non-Foliated minerals not Hornfels mud, mica parent rock varies visible Visible, medium to Parent rock is Quartz (SiO2) Quartzite coarse grains sandstone ROCK LAB IDENTIFICATION WORKSHEET Page ______ –
Intrusive Large crystals Primarily quartz, feldspar, muscovite, biotite Random crystals, colors vary, mostly from feldspars Granite Large crystals Plagioclase, hypersthene, olivine, augite Same material as basalt, slow to cool Gabbro Extrusive Fine grained – may be too fine to see crystals Plagioclase, hypersthene, olivine, augite Dark grey to black, difficult to break Basalt Fine grained, some scattered large crystals Primarily quartz, feldspars Usually light colored, may have gas bubbles Rhyolite Volcanic - Extrusive Large gas bubbles, Glass-like, Mineral grains uncommon Dark color, low density, blown from volcanoes Scoria Glass-like, cools too quick to form crystals Black glass Conchoidal fracture; may have white crystals Obsidian TYPE: SEDIMENTARY ROCKS Group Particle Size Composition Comments Rock Name Clastic Coarse grains, > 2 mm Any rock type (quartz common) Rounded fragments Conglomerate Fine grains, < 2 mm Quartz with other mineral fragments Color depends on other minerals, sandpaper feel Sandstone Very fine grains, too small to see Quartz and clay particles Formed from mud, has very thin but visible layers Shale Biological Varies, but usually fine grained Carbonaceous material From compacted, non-marine plants Lignite Fine grained Calcite Fizzes with vinegar Limestone Chemical Very fine grained gypsum Evaporate, pinkish color Gypsum TYPE: METAMORPHIC ROCKS Group Particle Size Composition Comments Rock Name Foliated Fine grained, minerals not visible From minerals with basal cleavage: Dense; thin pieces; parent rock is shale Slate Medium to coarse grained Feldspar, quartz, may have mica, iron minerals Light & dark color bands, parent rock granite or diorite Gneiss Medium to coarse grained Muscovite, biotite, feldspar, quartz, tourmaline, others Varieties named for major minerals; parent rock is phyllite Schist Non-Foliated Visible, medium to coarse grains Calcite (CaCO3) Parent rock is limestone Marble Fine grained, minerals not visible Clay minerals, mud, mica Dense, dark color, parent rock varies Hornfels Visible, medium to coarse grains Quartz (SiO2) Parent rock is sandstone Quartzite ROCK LAB IDENTIFICATION WORKSHEET – Page ______