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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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Web resources

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Vocabulary

fracture cleavage isometric prismatic onchodial crystal habit

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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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Hardness and cleavage

Hamblin; Howard, EPG, 2007.

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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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Electrostatic attraction between layers and not covalent / ionic bonding

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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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Very common rock forming minerals (like the classics)

elongated rectangular cleavage

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What type of cleavage is observed?

What are the three common rock forming minerals illustrated below?

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Another classic exampleelongated parallelogram cleavage

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How cleavage surfaces and what are the geometries (degrees)?

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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 interesting optical property of materials

rhombohedral cleavage

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Cleavage apparent (H ~4)octahedral cleavage

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Cleavage (not in The Rx Colln)

dodecahedral cleavage

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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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Twinning

NAGT

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Lamellae

Notice the fracture surface

Notice the cleavage surfacesWhat angle?

NAGT slide

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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