Geology Lab Quiz 1
how are minerals distinguished from one another
based on their unique combo of chemical composition and internal structure (chemical and physical properties)
specific luster
feeling and look
transparent
minerals that are so clear that you can almost read through them
opaque
minerals that do not allow any light to pass through them, even in the thinnest of specimens
uneven fracture
rough, irregular fracture surfaces
conchoidal fracture
smooth curved fracture surfaces, like glass
soft minerals
will not scratch glass, but can be scratched with a knife blade or masonry nail - hardness of 5.5 or less
prismatic cleavage (2)
elongated forms that fracture along short parallelogram cross-sections - 2 cleavages do not intersect at 90 degrees
prismatic cleavage
elongated forms that fracture along short, rectangular cross sections - 2 cleavages intersect at or near 90 degrees ex) potassium feldspar
rock-forming minerals
Minerals that make up most of the rocks of Earth's crust
color
Rocks generally have a 'typical' color. Variations in this color (tarnishing, clarity, weathering) can often help identify a rock.
hackly fracture
breaks along jagged surfaces like broken metal
translucent
let light pass through (non opaque)
density
mass per unit volume (g/cm^3)
fibrous fracture
separates into soft fibers, like cloth
cubic cleavage
shapes made of cubes and parts of cubes - 3 cleavages intersect at 90 degrees - ex) halite
splintery fracture
splinters like wood
striations
straight/fine "hairlike" grooves on the cleavage surfaces or crystal face of some minerals (ex = exsolution lamellae - the mix of light-colored sodium feldspar with darker colored potassium feldspar ex) polysynthetic twinning = parallel, hairline striations on cleavage faces such as with plagioclase feldspar)
crystal
term used when talking about the lattice structure or about mineral specimens that have nicely developed crystal faces
tenacity
the manner in which a substance resists pulling or breaking apart - how a mineral resists breaking - Brittle (shatters like glass), malleable (can be hammered or bent permanently into new shapes like modeling clay or gold), elastic or flexible (like a plastic comb - bends but returns to its original shape) , sectile (can be carved with a knife)
crystal faces
the planar, flat surfaces of a mineral grain that stopped growing when it was still in contact with gas or liquid - orientation of a each face on a mineral grain reflects the orientation of a particular plane in the crystal lattice
crystallography
the scientific study of the structure and symmetry of crystals - concerned with structure, not chemistry
basal (book) cleavage
"books" that split apart along flat sheets ex)talc - but too soft to be visible - 1 cleavage plane
luster
how light is reflects - the appearance of a mineral's surface in reflected light - physical property
fracture
Any break in a mineral that does not occur along a cleavage plane resulting in uneven, random breaks. - broken surfaces, lacking cleavage planes
magnetic
indicates presence of iron (Fe)
good cleavage
results in many small, obvious, flat, stair like parallel surfaces
graphite vs. diamond example
- the unique lattice structure makes the difference between graphite and diamonds - both carbon, but graphite is soft( H of 1) and black and diamonds are the hardest mineral and have a clear color
hard minerals
will scratch glass, but cannot be scratched with a knife blade or masonry nail - hardness of greater than 5.5
streak
• Color of a rock in powdered form. - color of a fine-grained powder of a mineral • Note that a streak plate is 6.5 on the Mohs Scale. --> a mineral with a hardness greater than this will not be able to be streaked on this plate - white plates for dark minerals, dark plates for light minerals - harder minerals can be crushed to a powder or dragged across a diamond file to determine their streak
metallic luster
• Reflect light similar to most common metals. • Opaque, reflective surface with a silvery, gold, brassy, or coppery sheen - light reflects from the outermost surface of a mineral lattice to produce metallic luster, which has a mirror-like quality ex) gold, silver, copper, pyrite, galena
non metallic luster
- Not reflective like metallic, but can still reflect light if a cleavage or habit surface. • Waxy, pearly, earthy, greasy, resinous, vitreous, silky, satin - generally light can penetrate at least a short distance into the crystal lattice before some of it reflects back out again - light can pass entirely through some nonmetallic hand specimens and can through all nonmetallic specimens if they are thin enough
habit
- is the natural shape of a mineral's crystals before any cleavage or fracture occurs.; general crystal forms (geometric shape) and combination • Most of the lab samples do not exhibit crystal forms (the geometric shape of a mineral, formed by intersecting flat, outer surfaces called crystal faces) because they are broken pieces of larger crystals • Unlike the crystal face, the cleavage plane tends to be smooth and shiny - wiry or fillform, twinned, needlike or acicurcular, bladed, radiating needles, fibrous (like asbestos), dendritic, tabular (like a book), botryoidal (grape-like masses with raditing needles inside) - shape of a mineral or of aggregates of the same mineral - shapes in which crystals are commonly found
Flourite
- luster = non metallic - hardness = 4 - cleavage = excellent, octahedral, 4 planes - color = light - purple, white, clear, blue, etc. (colorless, purple, blue, gray, green, or yellow) (transparent or opaque) - streak = white - other properties = variety of colors, oil stain, CaF2 (calcium flouride); crystals usually form cubes (habit); brittle - uses = ore of flourine used in flouride toothpaste, refrigerant gases, rocket fuel
Halite
- luster = non metallic - hardness = 2.5 (<5.5) (2.1- 2.6) - cleavage = cubic; 3 cleavage planes; excellent cleavage in 3 directions that intersect at 90 degrees, so breaks into cubes - color = clear, white, yellow, blue, brown, or red (colorless, white, yellow, blue, brown, or red; transparent or translucent) - streak = white - other properties = cubic habit; salty taste; NaCl; brittle - uses = table salt; road salt; sodium ore; used in water softeners and as a preservative
Calcite
- luster = non metallic - hardness = 3 - cleavage = rhombohedral; 3 planes & angles do not intersect at 90 degrees (3 excellent cleavages) - color = light/white (usually colorless, white, or yellow, but may be green, brown, or pink; opaque or transparent) - streak = white - other properties = reacts with HCl (effervesces); CaCO3 (calcium carbonate) - uses = make antacids tablets, fertilizer, cement; ore of calcium
apatite
- luster = non metallic - hardness = 5 - cleavage = none; conchoidal fracture - color = variety of colors, but often green (pale or dark green, brown, blue, white, or purple; sometimes colorless: transparent or opaque) - streak = white - other properties = hexagonal habit (forms hexagonal prisms) - uses = mostly to make fertilizer, pesticides, transparent varieties sold as gemstones
Gypsum
- luster = non metallic (earthy to pearly for alabaster; silky or satiny for satin spar) - hardness = 2 (very soft) - cleavage = good cleavage in 1 plane; poor cleavage in another plane - color = light (colorless, white, or gray; yellow also for the satin spar variety; transparent to translucent) - streak = white - other properties = soft enough to scratch with fingernail; tabular habit (forms tabular crystals, prisms, blades, or needles - satin spar variety); sulfate (hydrated calcium sulfate) (massive habit for satin spar variety) - uses = plaster-of-paris, wallboard, drywall, art sculpture medium (alabaster)
Talc
- luster = non metallic (silky to greasy) - hardness = 1 - cleavage = poor - does have basal cleavage but so soft it isn't visible (forms cryptocrystalline masses that show no cleavage) - color = light/white (white, gray, pale green, or brown) - streak = white - other properties = soapy or greasy feel, silicate, no habit; can scratch with you fingernail easily; hydrous magnesium silicate - uses = used as a "filler" (to take up space and reduce cost) in plastics for car parts, appliances, massive pieces carved into art sculptures
k-spar, potassium feldspar, orthoclase feldspar
- luster = nonmetallic - hardness = 6 - cleavage = prismatic; two cleavage planes that intersect at 90 degrees (nearly 90 degrees; excellent cleavage) - color = often pink (orange, brown, white, green, or pink; forms translucent prisms with sublateral exsolution lamellae) - streak = white - other properties = exsolution lamellae (in mineralogy, process through which an initially homogeneous solid solution separates into at least two different crystalline minerals without the addition or removal of any materials - makes it appear streaky due to presence of lighter, sodium rich feldspar with that of darker, potassium rich feldspar); silicate (potassium aluminum silicate); KAISi3O8 - uses = used to make ceramics, glass, enamel, soap, false teeth, scouring powders
Quartz
- luster = nonmetallic (greasy) - hardness = 7 - cleavage = none - color = light - many colors (usually colorless, white, or gray but uncommon varieties occur in all colors; transparent to translucent) - streak = too hard to determine (white - but too hard to determine with a streak plate because the hardness is over 6.5, they scratch the streak plate) - other properties = hexagonal habit; conchoidal fracture; SiO2 (silicon dioxide) - uses = as an abrasive; used to make glass, gemstones
Mohs Hardness Scale
A scale ranking ten minerals from softest to hardest; used in testing the hardness of minerals - diamond = hardness of 10 - higher numbered minerals will scratch lower numbered minerals - ranges 1-10 - fingernail = 2. 5 - Copper Penny = 3.5 - Knife/Glass Plate = 5.5 (glass plate - you scratch the mineral to the plate and if it scratches the glass then it is harder than 5.5) - Steel Nail = 6.5 - Masonry drill bit = 8.5
reaction to acid
carbonate minerals react when a drop of dilute HCl (the acid test) is applied to one of their freshly exposed surfaces - carbonate minerals will effervesce (fizz)
minerals
Inorganic, naturally occurring substances with definite chemical composition, distinctive physical properties, and crystalline structure - if you make it, it is not natural and cannot be considered a mineral (this includes usually solids that are generated by biological activity as well) (synthetic crystals are not mineral specimens because they are not formed by geologic processes) - a naturally occurring crystalline solid that has been formed by geologic processes, on Earth or elsewhere in the universe - distinct from one another by their well-defined chemical composition and crystal structure, which result in a unique set of physical properties that can be used to identify it - building block of rocks - physical foundation of both our planet (rock forming minerals) and human societies
submetallic luster
luster that seems intermediate between "metallic" and "nonmetallic"
cleavage
Tendency to break (cleave) along flat, parallel surfaces of weak structural planes. Often results in reflective surfaces/planes - flat surfaces on broken pieces = called cleavage planes & they coincide with surfaces of relatively weak chemical bonding in the crystal lattice - each different set of parallel cleavage planes = cleavage direction
hardness
a measure of a mineral's resistance to scratching - harder substance scratches a softer one
industrial minerals
main non-fuel raw materials used to sustain industrialized societies like ours
no cleavage
no parallel broken surfaces; may have conchoidal fracture (like glass) ex) quartz, apatite
crystalline solid
occur in a regular pattern that is repeated in three dimensions billions of times in even the smallest mineral grain that we can see (a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions)
identification flow chart
primary steps = luster -> hardness -> cleavage & fracture -> color & streak secondary steps = tenacity -> magnetic -> acid test -> habit & crystal form -> smell, taste, feel
mineral grain
refer to a particle composed of a single crystal of a mineral, however we find it - as a singular mineral specimen with well-developed crystal faces, as a broken piece of an individual crystal, as one crystal within an intergrown mass of crystals, or as a rounded sedimentary particle developed from a single crystal of mineral
lattice
regular geometric arrangement of atoms in a crystal - the 3-D geometry of a lattice controls the internal structure and the shape of the outer surface of any crystal
excellent or perfect cleavage
results in a set of obvious, large, flat, parallel cleavage surfaces
poor cleavage
results in a set of small, flat, parallel surfaces that are difficult to detect
dodecahedral cleavage
shapes made of dodecahedrons and parts of dodecahedrons - 6 cleavages intersect at 60 and 120 degrees
octahedral cleavage
shapes made of octahedrons and parts of octahedrons - 4 main cleavages intersect at 71 degrees and 109 degrees to form octahedrons, which split along hexagonal shaped surfaces; may have secondary cleavages at 60 and 120 degrees ex) flourite
rhombohedral cleavage
shapes made of rhombohedrons and parts of rhombohedrons - 3 cleavages do not intersect at 90 degrees ex) calcite
smell and taste
some minerals stand out to the senses