<p> Tables to Help Identify Rocks</p><p>CLASSIFICATION OF IGNEOUS ROCKS Composition Light-Colored Intermediate-Color Dark-Colored Very Dark Color 10-20% quartz No quartz No quartz 100% K-feldspar > plagioclase > plagioclase ≈ 50% ferromagnesian plagioclase K-feldspar 50% ferromagnesian minerals ≈10% 25–40% minerals ferromagnesian ferromagnesian minerals minerals Pegmatitic (very coarse- Pegmatite grained) Porphyritic (mixed crystal Porphyry sizes) Phaneritic Granite Diorite Gabbro e (coarse-grained) Granodiorite r u t</p><p> x Peridotite e Aphanitic Rhyolite</p><p>T Andesite Basalt (fine-grained) Dunite Glassy Obsidian Porous Pumice Scoria (glassy, frothy) Pyroclastic Volcanic tuff (fragments < 4mm) (fragmental) Volcanic breccia (fragments > 4mm)</p><p>CLASSIFICATION OF CLASTIC SEDIMENTARY ROCKS Particle size Rock Name Characteristics Conglomerate Rounded grain fragments Coarse (> 2mm) Breccia Angular grain fragments</p><p>Quartz grains Quartz (often well rounded, well sorted)</p><p>Quartz and feldspar grains Medium (1/16–2mm) Sandstone Arkose (often reddish color)</p><p>Quartz grains, Small rock fragments, Graywacke and clay minerals (often grayish color)</p><p>Silt sized particles, Fine (1/256–1/16 mm) Siltstone surface is slightly gritty Clay sized particles, Fine (< 1/256 mm) Shale surface has smooth feel, no grit</p><p>CLASSIFICATION OF METAMORPHIC ROCKS Foliated Metamorphic Rock Crystal Size Rock Name Characteristics Very fine, crystals not visible Slate Excellent rock cleavage Fine grains, crystals not visible Phyllite Well developed foliation; glossy sheen Muscovite schist Coarse texture Chlorite schist Crystals visible with unaided eye Biotite schist t Mineral content reflects s i</p><p>Micaceous minerals h Garnet schist increasing metamorphism c Often contains large crystals S Staurolite schist from top to bottom Kyanite schist Sillimanite schist Coarse Gneiss Banding of light and dark minerals</p>