Geology Exam 2 Ros-Hulman

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Law of constancy of interfacial angles

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Angles between corresponding faces crystal faces of the same mineral are always the same, holds true no matter what size crystals are measured

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Crystallographic axes

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The location of crystal faces on a crystal is quantified by their own orientation with respect to the crystallographic axes, which are imaginary lines drawn through the crystal connecting the centers of corresponding crystal faces on opposite sides of the crystal. All crystals have been grouped into six crystal systems based upon their geometrical properties.

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crystal habit: geometric shapes

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geometric shapes. The flat surfaces of these forms are called crystal faces. Crystal form/habits is an external feature of mineral crystals.

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cleavage

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Tendency to break along planes of weak bonding. Produces flat, shiny surfaces. Desribed by resulting geometric shapes, number of planes, angles between adjacent planes. breakage that takes place along regularly spaced planes of weakness caused by weak bonds in those directions within the internal structure.

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Fracture

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occurs in minerals that lack preferred directions of weakness. The surfaces of rupture are more irregular in these minerals

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Hardness

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The strength of atomic bonds, along with the size and the density of the packing of atoms or ions in a mineral, determines its hardness. Physical test used to determine the hardness of a mineral involves scratching it with various materials.

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mineral color

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*generally unreliable for mineral identification. Often highly variable due to slight changes in mineral chemistry. Exotic colorations of certain minerals produce gemstones.* Many minerals occur in a wide variety of colors. The property of color is caused by the absorption of selective wavelengths of white light. Impurities can supply color to the mineral.

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streak

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*Color of a mineral in its powdered form.* color of finely powdered mineral particles produced by scraping the specimen across a porcelain (streak) plate

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metallic luster

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a property that results from the manner in which light is reflected from a mineral. Metallic luster is caused by high surface reflectivity of light by the opaque minerals, minerals that strongly absorb light. (Native metals)

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nonmetallic luster

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Brilliant, reflective luster of diamond and other gems known as adamantine luster. Common glass and quartz exhibit vitreous luster.

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Extrusive

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Cooling of molten liquid flows to the surface (lava)

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Intrusive

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Cooling takes place below the land surface. Intrusion refers to the movement of magma from a magma chamber to a different subsurface location. Bodies of rock formed by the intrusion of magma are called plutons

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Texture Porphyritic Phaneritic *

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A porphyritic-phaneritic texture is characterized by two distinct crystal sizes, both of which can be seen with the unaided eye. The smaller crystals constitute a groundmass, or matrix, that surrounds the larger crystals.

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Texture Porphyritic Aphanitic

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A porphyritic-Aphanitic texture is defined as a rock having an aphanitic groundmass, or matrix, in which embedded phenocrysts make up more than 10% of the total rock volume. The phenocrysts are visible to the unaided eye. If phenocrysts are abundant, the rock may appear initially to be phaneritic. Careful observation of the area between the phenocrysts will indicate if there is in fact aphanitic matrix.

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Texture Glassy

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cooling is so rapid that crystallization is prevented. The silica tetrahedral are frozen in place before they can attain an orderly arrangement necessary for mineral growth. Cooling at these rates leads to the formation of glassy texture, the glass in this case being a natural, noncrystalline material.

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Rock: Obsidian

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rock composed primarily of volcanic glass. Most common rock with a glassy surface

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Rock: Breccia

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rocks formed from angular, coarse-grained pyroclastic material

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Tuff

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Rocks formed from volcanic ash

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Rock: Pumice*

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volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. Typically light colored. Created when super-heated, highly pressurived rock is violently ejected from a volcano. Rapid

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What are the four common detrital rocks

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1) Shale or mudstone: mud-sized particles in thin layers that are commonly referred to as laminae, most common sedimentary rock
2) Siltstone
3) Sandstone: composed of sand-sized particles, forms in a variety of environments, quartz is the predominant mineral
4) Conglomerate or Breccia: both are composed of particles greater than 2mm in diameter, conglomerate consists largely of rounded gravels; often has a similar appearance to “concrete”, breccia is composed mainly of large angular particles and fragments, which have not been rounded

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What are the three common chemical rocks

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1) Limestone: most abundant chemical rock, underlies much of MO, IN, KY, WV and TN. Composed chiefly of the mineral calcite, marine biochemical limetsones form as coral reefs, coquina (broken shells), and chalk microscopic organisms), inorganic limestones include travertine and oolitic limestone
2) Dolostone: Typically formed secondarily from limestone
3) Chert: composed of microcrystalline quartz, varieties include flint and jasper (banded form is called agate)

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Sedimentary facies:

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different sediments often accumulate adjacent to one another at the same time, each unit (called a facies) possesses a distinctive set of characteristics reflecting the conditions of a particular environment, the merging of adjacent facies is a gradual transition.

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Evaporites

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evaporation triggers deposition of chemical precipitates, examples include rock salt, gypsum, and potash. Coal: different from other rocks because it is composed of organic material.

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Texture Classic

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discrete fragments and particles, all detrital rocks have a clastic texture. Nonclastic: pattern of interlocking crystals, may resemble an igneous rock

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Texture crystalline:

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which are composed of crystals that grew together in an interlocking manner, like when a magma cools and solidifies

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Texture oolitic:

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The texture of a sedimentary rock consisting largely of ooliths showing tangential contacts with one another.
Spherical grains formed by precipitation of concentric layers or calcium carbonate in a shallow-water marine environment where waves or currents periodically roll grains across the bottom.

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Texture skeletal texture (or fish net)

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rapid crystallization
bio clastic debris includes the skeletal remains of organisms that secrete shells of calcium carbonate. Corals that build extensive reefs composed of intergrown netrwords of skeletal calcite and solitary organismslike clams and snails.

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Texture Fragmental

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Fragmental textures consist of broken, angular fragments of ejected igneous material, ranging from large blocks to fine dust. The rock may contain fragments of the wall rock surrounding the vent, but it is composed mostly of fragments of ash, pumice, and aphanitic rocks. materal finer than 4mm is called tuff , larger than 4mm is referred to as volcanic rock

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Textures Aphanitic

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individual crustals are so samll they cannont be detected without the aid of a microscope. Rocks of this texture appear massive and strureless but contain small interlocking crystals

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Texture Phaneritic

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are those in which individual crystals are large enought to be plainly visible to the naked eye

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Igneous Rocks

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Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.

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Sedimentary Rocks

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These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

sandstone, limestone, shale, congolomerate, gypsum

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Mineral Rocks

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These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

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intusive vs extrusive: what are engineering characteristics of unaltered intrusive igneous rocks versus extrusive rocks

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Igneous rocks which form by the crystallization of magma at a depth within the Earth are called intrusive rocks. Intrusive rocks are characterized by large crystal sizes, i.e., their visual appearance shows individual crystals interlocked together to form the rock mass. The cooling of magma deep in the Earth is typically much slower than the cooling process at the surface, so larger crystals can grow. Rocks with visible crystals of roughly the same size are said to have a phaneritic texture.

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intusive vs extrusive: what are engineering characteristics of unaltered intrusive igneous rocks versus extrusive rocks

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Broadly igneous rocks are divided in two categories 1) Extrusive Rock 2)Intrusive Rocks. Intrusive rocks, in general , have density 150-200(pcf) their compressive strength ranges form 3-30 (Psi*100). Usually the discontinuities found in these rocks are joints, Mostly tight joints, so the permeability and storage capacity is low. The extrusive rocks have density range from 120-200 (pcf) and their compressive strength ranges is 1-30(Psi*100).As these rocks are formed by the consolidation of lave on the surface of earth, and are exposed to the weathering agents more then the intrusive rocks, so these have many type of discontinuities in them, the most common are joints, voids and flow fractures. The presence of discontinuities increase the permeability and ability to store the fluids,mostly water. Hence its permeability is from low to high, depending upon the concentration of discontinuities.