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Name ____________________________________ Date ___________________ LAB ON METAMORPHIC ROCK IDENTIFICATION Metamorphic rocks are generally "prettier" than sedimentary rocks! This is because when metamorphic rocks break, they break through mineral grains thus exposing fresh bright surfaces. Sedimentary rocks tend to break around grains exposing an old weathered surface. Rocks defined by foliation: This means that there is some kind of layering or mineral streaking in the rock Microscopic grain size, tends to split in smooth flat surfaces with a slight sheen. Colors range from black to gray, to red and green Easy to scratch with the glass plate. Formerly shale. SLATE Grain size mostly microscopic but the surface tends to sparkle due to mica minerals that have been growing in size due to a longer period of metamorphism.. tends to break in smooth undulatory (wavy) surfaces. Formerly shale PHYLLITE Macroscopic grain size, mica flakes common, splits along an undulatory surface Commonly hard and soft minerals. Micas Biotite & Muscovite are common. May also contain quartz, garnet, hornblende Formerly fine grained sedimentary rocks. SCHIST Macroscopic grain size, distinct color layering or distinct streaks of darker and lighter minerals. Mostly hard minerals like quartz, feldspars and hornblende. The pre metamorphic rock may have been igneous, sedimentary or metamorphic rock. GNEISS Rocks defined by composition Sugary texture to coarse grained, SOFT - scratches easily with corner of glass plate and fizzes with acid. Can be many colors - white, pink, greenish even black. Formerly limestone Same as above, BUT only the powder fizzes in acid. Formerly dolostone Sugary texture, HARD - scratches glass easily. Usually has a clean sometimes sparkly appearance. Formerly quartz sandstone Black, smooth, concoidal breaking pattern and feels light If you toss it in your hand. Not common but a really cool rock. Formerly bituminous coal CALCITE MARBLE DOLOMITIC MARBLE QUARTZITE ANTHRACITE The Exercise: 1. Write the number of the specimens in numerical order. 2. Describe grain size and/or texture microscopic fine - less than .5 mm ( mm scale on reference chart) coarse - .5 mm to 2 mm very coarse - larger than 2 mm smooth 3. Color/hardness As well as color, will it scratch glass or glass scratch it? 4. Mineral composition and other properties. Quartz – translucent, hard, no cleavage Feldspar – hard, pink or white flat cleavage surfaces Hornblende – hard, flat cleavage surfaces, looks like black needles Garnet – red, glassy round nodules. You may see crystal faces Muscovite (white mica) – looks like silvery flakes Biotite (black Mica) – black and flaky Calcite - fizzes in HCl Dolomite - only powder will fizz 5. name the rock Other Rocks Observations or answers to questions ______________________________ ___________________________________________________ ___________________________________________________ ______________________________ ___________________________________________________ ___________________________________________________ ______________________________ ___________________________________________________ ___________________________________________________ ______________________________ ___________________________________________________ ___________________________________________________ ______________________________ ___________________________________________________ ___________________________________________________
