Lesson 2: Physical Properties of Mineral Flashcards
Crystal Form and Crystal Habit
- Morphology
- Form
- Habit
- Unit Cell
- Aggregate
- completely bounded by crystal
- growth during primary crystallization or recrystallization was not restrained or interfered with by adjacent grains, and the faces were not greatly affected by late physical or chemical erosion
Euhedral Crystals (idiomorphic or automorphic)
- partly bounded by crystal and partly by surfaces formed against pre-existing grains
- minerals were able to crystallize with their characteristic habit only in part, due to the presence of neighboring crystals that partly constrained their growth
Subhedral (ipidiomorphic)
- lacks crystal faces and shows rounded or irregular surfaces due to crowding of adjacent minerals
- e.g. embayed crystals with irregular outline, but also interstitial grains that grew in the space left between other, pre-existing crystals
Anhedral (xenomorphic or allotriomorphic)
The outward expression of the internal ordered atomic arrangement of a crystal
Morphology
Consists of a group of crystal faces which have the same relation to the elements of symmetry
Form
Includes the general shape of a crystal and its
growth irregularities
Habit
The smallest unit of structure that if stacked indefinitely in three dimensions would form the whole structure (further discussion in Crystallography)
Unit cell
Minerals whose crystals come in groups (e.g. thousands of crystals intimately intergrowing to form unique aggregate shapes)
Aggregate
For a crystal with one dimension markedly longer than the other two
Prismatic
With the external form of a rhombohedron
Rhombohedral
With the external form of a cube
Cubic
With the external form of an octahedron
Octahedral
With the pronounced development of one or more two-sided forms (pinacoid)
Pinacoidal
Crystals are roughly equidimensional
Equant
Flat and plate-like but crystals are typically thin and can be stacked on top of each other like sheets of paper
Lamellar
Flat and plate-like but have lengths and widths that are much larger than their thickness
Tabular
Crystals are elongated and flattened, like a knife blade, crystals are much longer than they are wide, and their width exceeds their depth
Bladed
Form as thin, flat sheets or flakes that are easily peeled or split off the larger mass
Micaceous
when edges are fully developed but the interior spaces are not filled in (hollowed-out step lattice formation)
Hopper
Crystal growth that produces fine, feathery scales from the Latin “pluma” = feather (fan-like or feather-like)
Plumose
needlelike, contains long, slender crystals which may radiate out like needles or bristles from a common base
Acicular
exhibits hairlike or threadlike filaments (Latin
“filum” = thread)
Filiform
exhibits clumps of sinewy, stringy, or hairlike fibers, the direction of growth is parallel to the longest dimension of the crystal
Fibrous
Crystals are interconnected in a network or lattice-like pattern (Latin “rete” = net)
Reticulated
Possesses several branches that radiate outwards from the center in a pattern resembling a star
Stellated
crystals have a branching, tree-like appearance, dendrites are formed when the crystals grow in a supercooled liquid (when liquid is below its freezing point but not yet frozen)
Dendritic
crystals are spherical, rounded, or bulbous
(Latin “collo” = glue)
Colloform
resembling a bunch of grapes (Greek “botrus”
=bunchof grapes
Botryoidal
crystals are rounded and have a bumpy or
knobby surface (Latin “mammilla” = nipple
Mammillary
displays the kidney shape (Latin “renes” kidney)
Reniform
spherical or oval-shaped and typically less than 4mm in diameter found in sed rocks (limestone & dolomite)
Oolitic
Develops round, pea-shaped forms and are larger and slightly more uneven than oolite (Greek “pisos” = pea)
Pisolitic
Tall, tapered, collum-like appearance of an icicle from the dripping of mineral-laden solution (Greek “stalaktos” = dripping)
Stalactitic
crystals are formed by the concentric deposition of mineral matter around a nucleus (rock, plant or animal remain, gas bubble, etc)
Concretionary
Crystals have parallel lines or grooves on their surface
Striated
Crystals are tightly packed together and form a kind of crust or coating on a surface
Drusy
Crystals grow in a direction that minimizes the surface energy of the crystal
Columnar
Large, lumpy mass with no apparent crystal form
Massive
Commonly given to describe the orientation of the form with respect to crystallographic axes
Miller Index
- Aggregates of similar crystals with their crystallographic axes and faces parallel
- represents a single crystal despite having the appearance of several crystals since its internal (atomic) structure remains unchanged in orientation
Parallel growth
- A symmetrical intergrowth of two (or more)
crystals of the same substance - the two or more individuals of the twinned aggregate are related by a symmetry element that is absent in the original (untwinned) crystal
Twin
➢ have a planar composition surface separating two individual crystals
➢ usually defined by a twin law that expresses a twin plane
➢ E.g. orthoclase twinned on the Braveno Law {021} as the twin plane
Contact Twin
Penetration Twin
➢ Have irregular composition surface separating two individual crystals
➢ usually defined by a twin center or twin axis
➢ E.g. orthoclase twinned on the Carlsbad Law, [001] as the twin axis
If the composition surfaces are parallel to one another
Polysynthetic Twins
if the composition surfaces are not parallel
to one another
Cyclical Twins
Refers to the general appearance of a mineral surface in reflected light
Luster
Like a metallic surface such as chrome steel, copper, and gold
Metallic
shown by light-colored minerals that transmit light, not metallic
Non metallic
The amount of light that a mineral can transmit
Diaphaneity
Capable of transmitting light and through which an object may be seen
Transparent
Capable of transmitting light diffusely
Translucent
Mineral that is impervious to visible light
Opaque
the striking flashes of varied color against a white or black background (e.g. opal)
Play of Color
Caused by light diffracted and reflected from closely spaced fractures, cleavage planes, twin lamellae, exsolution lamellae, or minute foreign inclusions in parallel orientation.
Iridescence
An optical phenomenon in which a band of reflected light, known as a “cat’s eye,” moves just beneath the surface of a cabochon-cut gemstone
Chatoyancy
- triple chatoyancy
- the result of scattering of light from inclusions in directions
Asterism
Any emission of light by a mineral that is no direct incandescence
Luminescence
A mineral that luminesces during exposure to ultraviolet light, x-rays, or cathode rays
Fluorescence
when a mineral exposed to ultraviolet light, x rays, or cathode rays continues to luminesce after the exciting rays are cut off
Phosphorescence
➢ Minerals like Quartz, Feldspars, Halite (10^-5 Slu)
➢ E.g. massive salt deposits that contrast with the positive magnetic susceptibility of the adjacent sedimentary rocks containing detrital magnetic grains
Diamagnetism
➢ Magnitude is inversely proportional to temperature (Curie’s law)
➢ Magnetic susceptibility ranges from 10^-3 to 10^-5 Slu
➢ Possessed by minerals like biotite, pyroxene, amphibole, olivine, and garnet
Paramagnetism
➢ Magnetism of ferrous metals (iron)
➢ At the Curie Temperature, ferromagnetic materials take on the properties of a paramagnetic material without the intense magnetism and the magnetic field memory
Ferromagnetism
➢ Most common form of magnetism causing magnetic anomalies
➢ Source of all magnetization in Earth materials
➢ Magnetite – principal naturally occurring ferrimagnetic component in the Earth
Ferrimagnetism
Mineral that breaks and powders easily
Brittle
A mineral that can be hammered out into thin sheet
Malleable
Mineral that can be cut into thin shaving with a knife
Sectile
Mineral that can be drawn into a wire
Ductile
Mineral that bends but does not resume its original shape when the pressure is released
Flexible
After the pressure is released, the mineral will
resume its original position
Elastic
