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Lecture 2 (Other Types (Specific Gravity (density), Taste and Smell, Feel,…
Lecture 2
Other Types
Specific Gravity
density
Taste and Smell
Feel
Magnetism
Reaction with a weak acid
Fluorescence
Colour
Some minerals have same chemical formula but differ in colour
due to impurities
due to variation of one of the elements in chemical formula
inclusions
colour transfer
electron trapped in a structural defect
reflection due to physical effects
opalescence
interference effects of reflected light
Some minerals have no variation in colour
Not diagnostic
colours based on our perception of colour
Types
Idiochromatic
Coloured by major element
Allochromatic
Coloured by impurities or minor elements
Diaphenity
How mineral transmits light
Twinning
Single crystals that grow off each other with symmetry
Types
Penetration Twins
irregular shaped composition surface
Pyrite
Contact Twins
regular shaped composition surface
octagonal surface, pentagonal surface
Quartz
Polysynthetic Twins
Composition surfaces all parallel
Multiple successive crystals forming
Albite
Cyclic Twins
Like polysynthetic but composition surfaces NOT parallel
Rutile
Composition Surface
Surface where the two crystals grow off symmetrically
Hardness
resistance to scratching
indicates internal structure and bond strength
Moh's Scale
relative scale for classifying hardness
logarithmic
Breakage
Cleavage
breakage along planes
planes form due to weaker bonding in atomic structure
Types
Basal
separates as plates
Mica
Cubic
three cleavages perpendicular to each other
Galena
Octahedral
four cleavages producing octahedral cleavage fragments
Fluorite
Prismatic
cleavages parallel to each other
Parting
breakage of twinned crystals
along composition surfaces
Fracture
undefined path of breakage
like dropped glass
Types
Even
smooth planar surfaces
Halite
Irregular
rough and irregular surfaces
Rhodonite
Hackly
jagged with sharp edges
Copper
Splintery
sharp splinters
kyanite, pectolite
Fibrous
fibres
chrysotile, crocidolite
Conchoidal
breaking with curved surfaces
glass-like
quartz
Shape
Form
Quality of the mineral's faces
Subhedral
Some defined crystal faces
Semi-sharp or rounded edges
Euhedral
Well defined faces
Sharp edges
"Crystal form"
Anhedral
no definite edges
no defined crystal faces
Depends on the atomic structure of the mineral
Habit
Overall shape of the crystal
Crystal Aggregates
Massive
not apparently special
Granular
grain-like composition
Radiating
radiating from a point
wheel and spoke pattern
Fibrous
fibre-like composition
Stalactitic
stalactite shaped
Stellated
star-like
Lamellar
slabs growing together
Plumose
feathery appearance
Dendritic
branch-like
Latticelike
slender crystals forming a lattice
Globular
spherical-like
Botryoidal
grape-like due to amount of individual minerals connected
Reniform
kidney shaped
Mamillary
breast shaped
Drusy
surfaces covered with fine minerals
Elliptic
small spheres
Individual Crystals
Blocky
square-like cross-sections
halite or galena
Acicular
needle-like
actinolite
Tabular
plates or sheets stacked together
gypsum or graphite
Capillary
vein-like
serpentine
Bladed
flattened elongated crystals
kyanite
Columnar
opposite faces parallel to each other
crystal-like
beryl
Micaceous
sheet-like
mica
Equant
nearly same dimensions in all directions
circle-like
garnet or spinel
Lustre
How light appears to reflect off a mineral
Types
Metallic
Sub-metallic
Non-metallic
Adamantine
diamond-like
high refractivity
brilliant lustre
Vitreous
like polished glass
emeralds or quartz
Resinous
resin-like
sphalerite
Pearly
like mother-of-pearl
talc or apophyllite
Greasy
oily-looking surface
microscopically rough surface
halite
Silky
silky or satin-like due to fibrous nature of mineral
fibrous gypsum
Earthy
dull
very fine grained
goethite or limonite
Streak
Colour of powder when mineral is scraped on a surface
Tenacity
Description of how it breaks, tears, or crushes
Brittle
breaks easily
vaporizes into powder easily
halite
Malleable
can be made sheet-like
copper
Sectile
separable into thin shavings
chalcocite
Ductile
can be made into wires
gold
Flexible
bendable but does not reform to original shape
talc, sheets of chlorite
Elastic
bendable and does reform to original shape
micas
Sheen
Reflected within material
Adularescence
reflection from sub-microscopic inclusions
Irridescence
reflection and interference from exsolved layers in feldspars
Schiller
Only reflection; no interference
Play of Colour
diffraction and interference of light through spheres of SiO2 in precious opal
Made by Nathan Hermawan