Geo 101 as they get Look at where eclogite stonally found at the Earth\'s surfac
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Geo 101 as they get Look at where eclogite stonally found at the Earth's surface. How can a dense rock, deep in a subduction ise ume surface? Activity 3: A Comprehensive Review Now that you have seen all three main types of rocks (igneous, sedimentary metamorphic), think about describing the characteristics of each group. Imagine you are holding the rock the yisual differences samples in your hand, and you are between the following examples. 1. How can you tell a rock from a mineral? . How can you tell a non-foliated metamorphic rock from a plutonic igneous rock? How can you tell a breccia or a conglomerate from a porphyritic rock? How can you tell a biochemical sedimentary rock from a fine-grained clastic sedimentary rock? (Remembe all biochemical sedimentary rocks have visible fossils.)Explanation / Answer
Minerals
Before you identify rocks, you have to be able to identify the minerals that make them up. Here's a strategy to follow. These are guidelines designed to get you to the most likely identifications fastest.
Geologic Setting
Sedimentary rocks
Common minerals: calcite, dolomite, gypsum, glauconite, celestite, barite, fluorite
Arid or well-protected settings: halides and sulfates, also be alert for borates, nitrates in extremely dry settings
Igneous rocks
Quartz never occurs with olivine, nepheline, leucite, melilite or corundum
Common minerals: Quartz, feldspars, pyroxenes, amphiboles, olivine, micas.
Granitic rocks may include epidote, tourmaline, beryl, apatite, topaz, zircon, and sphene
A pea-green mineral in granitic rocks is almost always epidote.
An intensely black mineral, especially with elongated crystals, is most likely tourmaline. A rounded triangular cross-section clinches it. Tourmaline is far deeper black than biotite, pyroxene, or amphibole.
In pegmatites, you may find lithium and rare-earth minerals.
Mafic rocks may contain calcic plagioclase, pyroxenes, amphiboles, olivine, nepheline, leucite, corundum, magnetite, spinel, or zeolites
Metamorphic Rocks
May include any minerals found in the parent rocks
Distinctive metamorphic minerals include:
Low temperature: chlorite, talc, chloritoid
Low pressures: andalusite, cordierite
Medium temperatures: actinolite, tremolite, epidote, diopside, anthophyllite, cummingtonite
High temperatures: staurolite, garnet, kyanite, sillimanite, wollastonite, forsterite, periclase, graphite.
High pressures: glaucophane, jadeite, lawsonite.
2. A non foliated igneous rock has only one mineral which contributes uniform in appearance.
Nonfoliated metamorphic rocks are formed around igneous intrusions where the temperatures are high but the pressures are relatively low and equal in all directions (confining pressure). The original minerals within the rock recrystallize into larger sizes and the atoms become more tightly packed together, increasing the density of the rock.
Nonfoliated metamorphic rocks are identified on the basis of their composition:
Quartzite = composed of the mineral quartz; metamorphosed sandstone
Marble = composed of the mineral calcite; metamorphosed limestone
Where as Plutonic Igneous Rock Igneous plutonic (or intrusive) rocks are those which have formed deep underground as magma cooled slowly over thousands of years following their emplacement. Such rocks have visible crystals (phaneritic texture). The rocks are classified on the basis of the proportions of the feldspar family of minerals, quartz, and the various dark (iron-rich) minerals like biotite, hornblende, augite and olivine. The felsic plutonic rocks usually have quartz, large proportions of potassium feldspar (orthoclase), and lesser amounts of plagioclase and mafic minerals. Intermediate and mafic rocks have increasingly larger proportions of dark iron-rich minerals. Ultramafic minerals have large significant amounts of the most iron-rich rock-forming mineral olivine.
Based on above description we can differentiate.
3. Breccia and conglomerate are very similar rocks. They are both clastic sedimentary rocks composed of particles larger than two millimeters in diameter. The difference is in the shape of the large particles. In breccia the large particles are angular in shape, but in conglomerate the particles are rounded.
4. Mainly can be differentiated by reaction with 10% HCL.
Biochemical sedimentary rocks are formed from organic processes that involve living organisms producing the sediments. These living organisms can be snails and clams whose discarded calcium carbonate shells can form limestone.Cemented shells of marine organisms form biochemical sedimentary rock.
Where as the finergrained clastic sedimentary rocks are called shale, siltstone, and mudstone. Shale is a smooth, thinly layered rock that is made up of finegrained silt and clay particles. Shale is considered a fissile rock because it splits very naturally along its layers. A siltstone contains mostly silt grains and looks very similar to shale but is not as fissile. Mudstone, the finestgrained clastic rock, is not well layered, and contains more clay than does shale or siltstone. Most shales, siltstones, and mudstones are tan, brown, gray, or black.
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