Geology Lab Midterm

seemingly random pattern along curved or irregular surfaces.

the ability of a mineral to resist being scratched.  This is measured by Mohs

Hardness Scale:

1) Talc         6) Orthoclase / Feldspar

2) Gypsum  7) Quartz

3) Calcite   8) Topaz

4) Fluorite  9) Corundum

5) Apatite  10) Diamond

color of the mineral powder left behind on the streak plate after you scratch the mineral/rock on the plate. not necessarily the same color as the mineral. ceramic streak plate has a hardness around 7 minerals harder than 7 will not leave a streak

the way that a mineral reflects light. The two basic categories of luster are metallic and nonmetallic, and nonmetallic can be further divided into glassy, pearly, greasy, earthy, shiny, dull.

Another way to distinguish between minerals is color, but since color alone will not distinguish an individual mineral, you must combine your observations with other physical characteristics.

Some minerals have an odor.  Example = Sphalerite (ZnS) which smells strongly of sulfur (rotten egg smell), others have a taste (example = Halite (NaCl – salt)).

Certain minerals like CaCO3 (calcite) react with dilute HCl (hydrochloric acid) by

effervescence or bubbling.

the silicon-oxygen tetrahedron (SiO)

rich in silicate and aluminum (Si, Al)

Quartz, Potassium- rich feldspar (orthoclase), Sodium calcium feldspar (plagioclase), muscovite (white mica), kyanite, sillimanite

rich in iron and magnesium (Fe, Mg)

Olivine, pyroxene, amphiboles, biotite (dark mica), Talc, serpentine

Fracture = conchoidal to subconchoidal

Hardness = 7

Luster = glassy to greasy

Color = colorless to gray

divided into two groups

1) orthoclase

2) plagioclase

both have properties = 2 directions of prominent cleavage, at nearly right angles, glassy to dull luster, H=6, range in color.

a) orthoclase feldspar tends to be pink if

it is in the same rock with plagioclase. b) plagioclase feldspar (if you have a fresh surface) may show

striations (fine parallel lines).

properties = all have excellent cleavage in one direction, H<2.5

Hardness = 1

greasy, slippery to the touch

Color = light colors in general

Streak =  white

Luster = pearly on surface where cleavage is present

muscovite and biotite are micas, both have a hardness around 2.5, they easily flake because they have excellent cleavage in one direction

Muscovite

Color= light(white, silvery, pale green)

Biotite

Color =generally dark brown, or black in color

generally dark in color, H = 6, and have 2 directions of cleavage. 

if pyroxene is seen from cross-section, the 2 planes of cleavage are very close to being right

angles

Color = pale green

Luster = vitreous

Hardness = 6

Crystals = fine grained

Rocks that are exposed at the earth’s surface are exposed to weathering and erosion

most commonly they are made up of carbonate sediment (calcite/ aragonite minerals). Shells and skeletons of marine creatures are often made of calcium

carbonate, so when these organisms die and fall to the ocean floor, they are

cemented by calcite to form limestone rocks.

minerals that precipitate out of solution via the process of

evaporation. (example = 2 on Moh’s hardness scale = gypsum, and halite)

break-down of rocks through physical processes

break-down of rocks through chemical alteration

diagenesis = physical/ chemical processes by which

sediment that is loose and unconsolidated is lithified.

changes in rock form occur when temperature and pressure are increased

large area metamorphism, with recrystallization occurring in the presence of

stress.

occurs in the area (contact) of an igneous intrusion, with recrystallization

occurring at high temperatures without stress being present

During recrystallization, boundaries between individual grains are adjusted, resulting in larger crystals,

when the new crystals interlock and become re-oriented, the texture of the rock changes.

orientation of platy minerals (remember how mica (biotite/muscovite) had sheet like cleavage planes making it have a platy appearance) into parallel planes (page 66 in your book shows a diagram). This is caused by stress (pressure) because the platy minerals become oriented perpendicular to the

direction of maximum stress.

interlocking crystals that are not oriented in a distinctly parallel orientation. Can form in both regional/ contact metamorphic rocks.  In regional metamorphic rocks, without a high percentage of platy minerals, the rocks will be non-foliated. In contact metamorphism, without direct stress, minerals

can become randomly oriented, called hornfelsic/ granoblastic.

these rocks break in into thin sheets because of the parallel orientation of small, platy mineral grains

parallel alignment of platy minerals that are coarse in texture

alternation of platy mineral bands that are foliated, with granular minerals

the holes that we saw in some igneous rocks (like basalt), can be filled by minerals during the process of recrystallization

when sedimentary rocks record layers of deposition, can be preserved and seen

as layering in metamorphic rocks

(as seen in porphyritic igneous rocks) or even fossils can be replaced by new

minerals during metamorphism, but the relict (leftover) textures can still be seen

the product when lava solidifies.

it forms an igneous body

called a pluton underground.

size and arrangement of the crystals, it

is controlled by the rate of cooling.

large interlocking crystals called phaneritic texture,

which is controlled by slow cooling.

small crystals, some glass which is called aphanitic texture, which is formed by rapid cooling. Sometimes, large crystals called phenocrysts, can be found

within a matrix of smaller crystals, this texture is called porphyritic. If magma cools very quickly, as in the case with volcanic rocks, the bubbles formed by the dissolved gases within the magma will leave

small trace holes called vesicles.

texture (in order to determine whether the rock is

plutonic or volcanic in origin) and composition: mafic, ultramafic, intermediate, or felsic.