is the way a mineral grows or how it is shaped/ the way it looks
when growth is unimpeded. Under ideal conditions, minerals tend to grow with relatively
smooth, exterior plane surfaces, and that is what we call the crystal face.
how the mineral breaks along a plane of atomic weakness. When you think of
cleavage remember that it is produced when the mineral is BROKEN.
seemingly random pattern along curved or irregular surfaces.
the ability of a mineral to resist being scratched. This is measured by Mohs
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.
Basic component (building block) of silicate structures
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
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).
Muscovite, Biotite, and Talc
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
Color= light(white, silvery, pale green)
Color =generally dark brown, or black in color
Pyroxenes and Amphiboles
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
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
What is a non-detrital sediment composed of?
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
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.
What is it called when the magma solidifies before reaching the surface?
it forms an igneous body
called a pluton underground.
what does the texture of an igneous rock refer to?
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.
How are we going to classify igneous rocks?
texture (in order to determine whether the rock is
plutonic or volcanic in origin) and composition: mafic, ultramafic, intermediate, or felsic.
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