Geology Lab Practical

  • luster definition :: an assessment of how light reflects off of unweathered, freshly broken mineral surfaces other than color

  • metallic luster description :: like that of metal

  • metallic luster examples :: gold, silver, copper

  • adamantine luster description :: like that of diamond

  • adamantine luster examples :: diamond

  • vitreous luster description :: like that of glass

  • vitreous luster examples :: fluorite, quartz, mica

  • greasy luster description :: like that of grease

  • greasy luster examples :: quartz

  • pearly luster description :: like that of pearl

  • pearly luster examples :: mica, talc

  • waxy luster description :: like that of wax

  • waxy luster examples :: serpentine, talc

  • dull luster description :: like that of chalk

  • dull luster examples :: clay

  • cleavage definition :: describes a mineral’s tendency to break along smooth, flat, shiny surfaces (planes)

  • basal cleavage description :: 1 plane of cleavage, forms flat fragments or flakes with ragged edges

  • prismatic cleavage description :: 2 planes of cleavage (often the most difficult cleavage to identify)

  • cubic cleavage description :: 3 planes of cleavage intersecting at right angles

  • rhombic cleavage description :: 3 planes of cleavage NOT intersecting at right angles

  • octahedral cleavage description :: 4 planes of cleavage (often forms triangular cleavage faces)

  • basal cleavage examples :: muscovite, biotite, talc, chlorite, graphite

  • prismatic cleavage examples :: feldspars, amphiboles, pyroxenes

  • cubic cleavage examples :: halite, galena

  • rhombic cleavage examples :: gypsum, calcite

  • octahedral cleavage examples :: fluorite

  • fracture definition :: a break that does NOT yield a smooth flat surface

  • uneven fracture description :: fracture yields a rough, irregular surface

  • conchoidal fracture description :: fracture yields a smooth, often shiny, curved surface

  • uneven fracture examples :: olivine, quartz, magnetite, chalcopyrite, hematite, pyrite

  • conchoidal fracture examples :: obsidian

  • parting definition :: a breakage between individual crystals rather than through them

  • parting examples :: fibrous parting of asbestos, the basal parting of corundum, flaky parting of graphite, chlorite, and talc

  • habit definition :: a mineral’s particular mode of occurrence

  • habit examples :: granular, fibrous, platy, or massive crystalline aggregates

  • massive definition :: describes aggregates of microscopic crystals that grow together forming a compact featureless mass with no preferred parting

  • massive aggregates examples :: kaolinite, pyrite, and hematite

  • octahedral simple terms :: like a gem

  • basal simple terms :: flat, smooth layers

  • rhombic simple terms :: cube but tilted

  • cubic simple terms :: boxy and square

  • prismatic simple terms :: 4 obvious flat sides, two uneven/bumpy; mostly flat except for two sides

  • conchoidal simple terms :: very smooth parts with circular design on smooth face like a vinyl

  • uneven simple terms :: looks random, like a “rock,” bumpy all over with no obvious sides

  • euhedral :: bordered by a set of crystal faces that are generally very smooth, flat shiny surfaces (not cleavage planes!!), given enough room to grow

  • anhedral/subhedral :: distorted crystals that interfered with each other when growing usually due to cramped growing conditions

  • euhedral commonly occurring minerals :: quartz, fluorite, pyrite, garnet, gypsum

  • hardness :: a mineral’s resistance to abrasion and is related to bond strength between ions

  • fingernail hardness :: 2.5

  • glass plate hardness :: 5.5

  • color :: a physical property that is a function of the wavelengths or frequencies of visible light preferentially reflected and absorbed by a material

  • chromophore :: a type of atom that strongly absorbs light (only needs to be present in trace amounts to color a mineral)

  • streak :: the color of a mineral’s powder, one per mineral

  • fluorite streak :: white

  • hematite streak :: brick red to reddish brown

  • specific gravity :: the ratio of the weight of a specimen to the weight of an equal volume of water; the more dense the greater the specific gravity

  • tenacity :: the measure of the toughness of a mineral or the manner in which it will deform under stress (crush, bend, tear, change shape, etc.); not the same as hardness

  • brittle tenacity definition :: crushes easily into fragments

  • malleable tenacity definition :: can be pounded into flat sheets

  • elastic tenacity definition :: will bend, but regains original shape when stress is released

  • flexible tenacity definition :: will bend and stay bent once the stress is released

  • brittle tenacity examples :: most minerals

  • malleable tenacity examples :: gold

  • elastic tenacity examples :: biotite and muscovite

  • flexible tenacity examples :: flakes of talc, graphite, and chlorite

  • pyroxene :: mineral, vitreous dark green to black color, prismatic cleavage at 90 degrees

  • biotite :: mineral, vitreous, dark colored mica, basal cleavage, flat flaky

  • plagioclase :: mineral, vitreous, white to grey, prismatic 90 degree cleavage, may have striations

  • orthoclase :: mineral, vitreous, pink red color, prismatic 90 degree cleavage

  • kaolinite :: mineral, dull and earthy, no cleavage, earth odor when wet, greasy feel, white and chalky

  • muscovite :: mineral, vitreous, light/clear color, basal cleavage, light colored mica, flat flaky

  • amphibole :: mineral, vitreous, black color, prismatic cleavage NOT at 90 degrees, often stepped cleavage planes

  • calcite :: mineral, vitreous, white or clear color, rhombic cleavage, reacts with HCL

  • quartz :: mineral, vitreous, clear/white/purple/pink/smoky color, uneven fracture, hardness of 7

  • olivine :: mineral, vitreous, GREEN, uneven fracture, granular aggregate, sugary texture

  • halite :: mineral, vitreous, cubic cleavage, white or clear color, salty taste

  • gypsum :: mineral, vitreous to pearly, rhombic cleavage (1 prominent direction), brittle sheets

  • galena :: mineral, metallic, cubic cleavage, silver grey color, SG 7.6

  • graphite :: mineral, metallic, greasy feel, will write on paper

  • talc :: mineral, pearly or waxy, basal cleavage, green/grey/white, greasy or soapy feel

  • pyrite :: mineral, metallic, uneven fracture, brass yellow, often cubic crystals, sometimes striated faces

  • hematite :: mineral, dull and earthy, uneven fracture, red to brown streak, can also occur metallic

  • chalcopyrite :: mineral, metallic, bronze to brassy yellow

  • magnetite :: mineral, metallic, dark grey to black color, uneven fracture, STRONGLY MAGNETIC

  • fluorite :: mineral, vitreous, octahedral cleavage, clear/purple/green/blue/yellow color

  • obsidian ::

  • pumice ::

  • granite ::

  • rhyolite ::

  • welded tuff ::

  • scoria ::

  • peridotite ::

  • diorite ::

  • basalt ::

  • gabbro ::

  • vesicular basalt ::

  • andesite ::

  • andesite porphyry ::

  • crystalline definition ::

  • glassy definition ::

  • phaneritic definition ::

  • aphanitic definition ::

  • porphyritic definition ::