Rock Identification Rock Lab 1

Identification of all three rock groups is based on Love it, Learn it, Live it , be one with it! Identification of all three rock groups is based on TEXTURE and COMPOSITION what the rock is made out of – type of minerals the appearance of the rock

Igneous Rock Classification Let’s form an igneous rock Two major types of igneous rocks Intrusive – magma solidifies below the Earth’s surface magma cools very slow crystals form interlocking “mosaic” textures very coarse-grained visible minerals referred to as Plutonic rocks Extrusive – magma solidifies above the Earth’s surface magma cools very fast minerals can not be seen with un-aided eye very fine-grained texture (no visible minerals referred to as Volcanic rocks

Textures of Igneous Rocks Igneous Rock Classification Identification of igneous rocks is based on two main characteristics Texture – the appearance of the rock due to the rate of magma cooling Composition – the type of minerals found in the rock (mineral composition) Textures of Igneous Rocks Intrusive rocks (Textural terms) phaneritic texture – crystals are visible and form a mosaic of interlocking mineral aggregates (less than 1 cm) Interlocking crystal grains phaneritic texture

Extrusive Igneous Rocks (textural terms) aphanitic texture – crystals are too small to see See, you really can not see any mineral crystals glassy texture magma cooled extremely fast (quenched) not enough time for atoms to combine (amorphous solid)- lacks a crystalline structure

Igneous Rock Classification Lab Vesicular texture- sponge like appearance, texture contains numerous cavities or holes Vesicles – gas bubbles cavities Pyroclastic texture – textures created by rapidly cooling lava that is “hurled” through the air picking up fragments (tuffaceous texture) rock fragments – pieces of rock “incorporated” into the rock (tuffaceous)

Igneous Rock Classification Lab Igneous Rock Composition mineral composition = mineral assemblages= chemistry The mineral is either ferromagnesian (dark colored) or felsic (light colored ferromagnesian (mafic) minerals rich in Fe, Mg – creates a dark colored rocks Pyroxene (Augite) Amphibole (hornblende) Mica - Biotite

Igneous Rock Classification Lab Igneous Rock Composition Mineral composition = Mineral assemblages = Chemistry The mineral is either ferromagnesian (dark colored) or felsic (light colored) Felsic – mineral composition is light colored minerals Ca-plagioclase K-feldspar (orthoclase) Mica- muscovite Quartz

Texture Origin Intrusive Extrusive X Igneous Rock Classification Felsic Mafic 80% Origin Texture 40% 20% Rock Descriptions Very coarse crystal grains, usually all grains are approximately the same size w/ respect to each other. Grains> one inch Coarse Very Granite Pegmatite Mafic Pegmatite Intrusive A mosaic of coarse-grains that are easily visible to the unaided eye – grains greater than 1 mm Phane- ritic Grano- diorite Diorite Gabbro Peridotite Granite Aphan- itic Fine to very fine grains, usually to small to be distinguished with the unaided eye or even with a hand lens Rhyolite Dacite X Andesite Basalt Glassy Glassy – non-crystalline, non-granular Color varies between black and brown Obsidian Extrusive Por- ous Highly vesicular, finely crystalline to glassy Pumice (light), Scoria (dark) Pumice Scoria Composed of fragments of all sizes Produced in volcanic environments, Ash Partially re-fused or cemented Rhyolitic Tuff Basaltic Tuff mental Frag-

Sedimentary Rock Identification Lab Sandstone Arches

How is a sedimentary Rock formed??? Why is the earth’s surface 75% sedimentary rocks????????? Erosion Pre-existing Rock Sediment Water, Wind, Ice Breaks down Pre-existing rock Rivers Deposited Transported Lakes Lithified Compacted Cemented Sedimentary Rock

Three major categories of Sedimentary Rocks Clastic Sedimentary rocks Chemical Sedimentary rocks Bio-chemical (bio-clastic) Sedimentary rocks

Clastic (inorganic-detrital) rocks are composed of particles or grains. Rock name is dependent on grain size. Decreasing grain size 2+ mm 2 mm 1/16 mm 1/256 mm

Chemical Rocks – inorganic, non-clastic rocks that are commonly the result of evaporation and precipitation Chemical rocks contain no fossils, or biological material but may react with HCl The Great Salt Lake, Utah halite (salt) crystals Calcium Carbonate (CaCO3) chemical rocks (evaporation / precipitation processes) Chemically precipitated SiO2

Bio-chemical (bio-clastic, biogenic) rocks – result from animal and plant secretions. The term clastic indicates that these rocks contain fossils or parts of plants shells, compacted plat material Animal parts Cemented shell fragments Lithified plant material

Classification Procedure Step 1: Determine if the rock is clastic or non-clastic Step 2: If the rock is clastic, determine the grain size and diagnostic properties. Make the ID. Step 3: If the rock is not clastic, determine if the rock is either chemical or bioclastic chemical – will not contain particles such as grains and organic material. Test rock to observe fizzing (carbonates) Match diagnostic properties on chart for ID bio-clastic- rock will be composed of particles that are organic- animal parts, plant secretions. Test rock to observe fizzing (carbonate) Match diagnostic properties on chart for ID

Metamorphic Rocks Meta (to change) morphic (form) = to change form Metamorphism– to change a rocks compositional and textural characteristics by subjecting the rock to various pressure/temperature relationships Rocks undergo a solid-state-transformation The parent rock: represents the pre-existing rock metamorphism Example: Shale (parent) Schist Limestone (parent) Marble 17

FOLIATED Identification of Metamorphic Rocks Identified by using the rocks Texture and Composition Compositional characteristics – types of mineral present common minerals: quartz, feldspar, muscovite special minerals: talc, garnet, chlorite related to P/T relationships Textural characteristics – minerals are oriented in various degrees of “parallelism” platy sub-parallel parallel FOLIATED Grain size distribution – fine-grain to coarse-grain reflects P/T relationships fine-grain coarse-grain Low P/T High P/T 18

Slaty Schistose Gneissic Fine-grained Coarse-grained Low P/T High P/T “compressed” layering - platy Parallel to sub-parallel Mineral alignment Alternating light and dark mineral bands Fine-grained Low P/T Coarse-grained High P/T

NON-FOLIATED Textural characteristics Non-foliated texture – minerals are not visible and there orientation does not exist Rock is composed of single type chemistry. NON-FOLIATED Example: rocks composed of CaCO3 rocks composed of SiO2 20

How can one Tell the Difference ? Shows NO foliation Composed of ONE COMPOSITION How can one Tell the Difference ? Quartz SiO2 Calcite CaCO3 “Fussed glass” Scratches glass Hard H = 7 “Sometimes xln” Fizzes in HCl Soft H = 3 Plant Material C -carbon

Classification Procedure Step 1: Determine if the rock is foliated or non-foliated does the rock contain “parallelism” or grains does the rock consist of a single chemistry with no visible grains? Step 2: If the rock is foliated examine the degree of “parallelism” examine the grain-size distribution refer to charts for ID Step 3: If the rock is non-foliated determine the composition of the rock determine the special characteristics Refer to charts for ID 22