Post on 22-Dec-2015
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How can we differentiate the rock forming minerals quartz (SiO2) from calcite (CaCO3)?
Professor Howard Lee McLeanDepartment of ChemistryRose-Hulman Institute of
Technology
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Defintions ___ the shape in which a mineral’s individual
crystals or aggregates of crystals growth (NaCl on a string; body salt)
___ geometric pattern generated because of the crystal’s tendency to break along flat planar surfaces
___ nongeometric pattern generated because of breakage along irregular surfaces
___ wavy breakage
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Crystal habit – covalent and ionic bonds control neighbors
garnet (garnet schist) isometricwell formed or rounded conchoidal fracture or irregular fracture
quartz check cover of Mineralogy book
single to six-sided primatic to massive crystals conchodial fracture to nondetectable
cleavage tenacity – brittle
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How prominent is the cleavage?Mineral cleavage (vs. rock cleavage)
one direction muscovite . biotite two directions (|) K-felspar . Ca-feldspar two directions amphipole . pyroxene three directions (|) halite three directions calcite four directions fluorite six directions sphalerite
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Cleavage is the tendency of a crystal to break along a
flat planar surface or zone of weakness. decreases with bond strength bond strength is low, cleavage is good -- mica bond strength is high, cleavage is poor --
quartz is classified according to primary attributes:
number of planes and pattern of cleavage quality of surface and ease of cleaving
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Cleavage
reflects light like a mirror results from planes of weakness within the
crystal structure along which the crystal breaks.
in contrast, crystal faces reflect the geometry of the atomic structure (crystal habit)
cleavage planes reflect light in a particular direction; whereas fracture surfaces reflect light in all directions
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Flaky minerals and their zone of weakness between layers
What mica exhibits one dimensional cleavage along zone of bonding weakness?
basal cleavage
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How many cleavage planes? Identify specimens in TRC
What are THREE positive tests and one negative test used to id?
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What type of cleavage is observed?
What are the three common rock forming minerals illustrated below?
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Halite (sylvite) type cleavage and common optical property
cubic cleavage
This mineral also exhibits a cubic crystal habit. This may be confusing.Transparent to translucent optical property.
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Cleavage and minerals
micas (biotite, muscovite, vermiculite) feldspars (K to Na to Ca-feldspar) amphiboles (horneblende; cl ~560 and
1240) pyroxenes (cl ~ 900) carbonates (calcite, malachite) sulfides (pyrite, galena, chalcopyrite)
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Less pronounced
talc one perfect and flaky type texture (slippery feel) foliated and very small aggregates
gypsum one perfect, splitting to distinctive slab usually two well pronounced, slabs or sheets granular, earth and finely crystalline masses, or even
tabular crystals magnetite
occasional octahedral isometric crystal habit conchodial or irregular fracture
hematite no fracture or uneven, splintery fracture