SES4U
Unit: Earth Materials
Mineral Identification
STREAK
The streak (also called "powder color") of a mineral is the color of the
powder produced when it is dragged across an un-weathered surface.
Unlike the apparent color of a mineral, which for most minerals can vary
considerably, the trail of finely ground powder generally has a more
consistent characteristic color, and is thus an important diagnostic tool in
mineral identification. If no streak seems to be made, the mineral's streak is
said to be white or colorless.
LUSTRE
Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back
to the latin lux, meaning "light", and generally implies radiance, gloss, or brilliance. Lustre varies over a wide continuum,
and so there are no rigid boundaries between the different types of lustre. (For this reason, different sources can often
describe the same mineral differently. This ambiguity is further complicated by lustre's ability to vary widely within a
particular mineral species.) The terms are frequently combined to describe intermediate types of lustre (for example, a
"vitreous greasy" lustre).
Adamantine “brilliant shine”
Ex. diamond
Metallic
“ polished”
Ex. pyrite
Silky “ Fibre like parallel grains”
Ex. Gypsum
Dull
“earthy, no shine”
Ex. kaolinite
Pearly “ thin reflective sheets”
Ex. muscovite
Vitreous “ glassy”
Greasy “resemble fat or grease”
Ex. opal
Resinous “ Smooth Plastic”
Ex. Amber
Waxy “ self-explanatory”
Ex. Jade
Ex. Quartz
SES4U
Unit: Earth Materials
CLEAVAGE
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural
planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal,
which create smooth repeating surfaces that are visible both in the microscope and to the naked eye.
Basal or pinacoidal cleavage occurs parallel to the base of a crystal.. Basal cleavage is exhibited by
the mica group and by graphite.
Cubic cleavage occurs on the faces of a cube for a crystal with cubic symmetry. This is the source of the cubic
shape seen in crystals of ground table salt, the mineral halite. The mineral galena also typically exhibits perfect
cubic cleavage.
Octahedral cleavage forms octahedra shapes for a crystal with cubic symmetry. Diamond and fluorite exhibit
perfect octahedral cleavage.
Rhombohedral cleavage occur as parallel faces of a rhombohedron. Calcite and other carbonate
minerals exhibit perfect rhombohedral cleavage.
Rhombohedral
MAGNETISM
Magnetic or nonmagnetic. Can be tested by using a magnet or a compass. Usually an indication of the iron
content in the specimen
SES4U
Unit: Earth Materials
HARDNESS
The Mohs Hardness Scale is the main scale to measure mineral hardness. Finger nail is 2.5, copper coin is 3.5,
glass is 5.5 and steel is 6.5. Hardness scale is measured by scratching a sample with other samples of known
hardness.
Talc is 1, Gypsum is 2, Calcite is 3, Fluorite is 4, Apatite is 5, Orthoclase Feldspar is 6, Quartz is 7, Topaz is
8, Corundum is 9 and Diamond is 10.
REACTIVITY
Is the mineral reactive or nonreactive? If it is reactive it usually has calcium carbonate composition ( component of
sedimentary rock formed from shells). Test is completed by dropping acidic solution onto sample and observing for
the release of gases/bubbling.
FLUORESCENCE
Gemstones, minerals, may have a distinctive fluorescence or may fluoresce differently under short-wave ultraviolet,
long-wave ultraviolet, visible light, or X-rays. Many types of calcite and amber will fluoresce under shortwave UV,
long-wave UV and visible light. Test is completed by exposing sample to UV light.
OPTICAL CLARITY/ TRANSMISSION
Transparency (3) is the physical property of allowing light to pass through the material without being scattered. A
translucent(2) medium allows the transport of light while a transparent medium not only allows the transport of light
but allows for image formation. Materials which do not transmit light are called opaque(1). Many such substances
have a chemical composition which includes what are referred to as absorption centers. Many substances are
selective in their absorption of white light frequencies. They absorb certain portions of the visible spectrum while
reflecting others. The frequencies of the spectrum which are not absorbed are either reflected back or transmitted
for our physical observation. This is what gives rise to color. The attenuation of light of all frequencies and
wavelengths is due to the combined mechanisms of absorption and scattering.
SES4U
CRYSTAL HABIT
Habit
Unit: Earth Materials
Image
Description
Acicular
Common Example(s)
Natrolite, Rutile
Amygdaloid
Almond-
al
shaped
Heulandite, subhedral Zircon
Blade-like,
Bladed
slender and
Actinolite, Kyanite
flattened
Botryoidal o
r globular
Grape-like,
hemispherical
masses
Hematite, Pyrite, Malachite,Smithsonite, Hemimorphite,
Adamite, Variscite
SES4U
Unit: Earth Materials
Similar to
fibrous: Long,
Columnar
slender prisms
Calcite, Gypsum/Selenite
often with
parallel growth
Aggregated
Coxcomb
flaky or tabular
crystals closely
Barite, Marcasite
spaced.
Cubic
Cube shape
Pyrite, Galena, Halite
Tree-like,
Dendritic or
arborescent
branching in
one or more
direction from
central point
Romanechite and other Mn-oxide minerals, magnesite,
nativecopper
SES4U
Dodecahed
ral
Unit: Earth Materials
Rhombic
dodecahedron,
Garnet
12-sided
Aggregate of
Drusy or
minute crystals
encrustatio
coating a
n
surface or
Uvarovite, Malachite, Azurite
cavity
Mirror-image
habit
(i.e. crystal
Enantiomor
phic
twinning) and
optical
Quartz, Plagioclase, Staurolite
characteristics;
right- and lefthanded
crystals
Equant,
stout
Length, width,
and breadth
roughly equal
Olivine, Garnet
SES4U
Fibrous
Filiform or
capillary
Unit: Earth Materials
Extremely
slender prisms
Serpentine group, Tremolite (i.e.Asbestos)
Hair-like or
thread-like,
many Zeolites
extremely fine
Foliated or
Layered
micaceous
structure,
or lamellar
parting into thin
(layered)
sheets
Mica (Muscovite, Biotite, etc.)
Aggregates of
Granular
anhedral
crystals in
Bornite, Scheelite
matrix
Doubly
Hemimorph
ic
terminated
crystal with two
differently
shaped ends.
Hemimorphite, Elbaite
SES4U
Hexagonal
Unit: Earth Materials
Hexagon shap
e, six-sided
Quartz, Hanksite
Like cubic, but
outer portions
Hopper
crystals
of cubes grow
faster than
Halite, Calcite, synthetic Bismuth
inner portions,
creating a
concavity
Breast-like:
surface formed
by intersecting
partial
spherical
Mammillary
shapes, larger
Malachite, Hematite
version of
botryoidal, also
concentric
layered
aggregates
Shapeless, no
Massive or
distinctive
compact
external crystal
shape
Limonite, Turquoise, Cinnabar,Realgar
SES4U
Unit: Earth Materials
Deposit of
Nodular or
tuberose
roughly
spherical form
Chalcedony, various Geodes
with irregular
protuberances
Octahedron,
Octahedral
eight-sided
(two pyramids
Diamond, Magnetite
base to base)
Plumose
Fine, featherlike scales
Aurichalcite, Boulangerite,Mottramite
Elongate,
prism-like:
Prismatic
crystal faces
parallel to caxis welldeveloped
Tourmaline, Beryl
SES4U
Unit: Earth Materials
Hexagonal
Pseudo-
appearance
hexagonal
due to cyclic
Aragonite, Chrysoberyl
twinning
Radiating
or divergent
Radiating
outward from a
Wavellite, Pyrite suns
central point
Similar to
botryoidal/mam
Reniform or
illary:
colloform
intersecting
Hematite, Pyrolusite, Greenockite
kidney-shaped
masses
Crystals
Reticulated
forming net-like
intergrowths
Cerussite
SES4U
Unit: Earth Materials
Rosette or
lenticular
Platy, radiating
(lens
rose-like
shaped
aggregate
Gypsum, Barite (i.e. Desert rose)
crystals)
Sphenoid
Wedge-shaped
Sphene
Forming as
stalactites or
Stalactitic
stalagmites;
Calcite, Goethite
cylindrical or
cone-shaped
Stellate
Star-like,
radiating
Pyrophyllite, Aragonite
Not a habit per
se, but a
condition of
Striated
lines that can
grow on certain
crystal faces on
certain
minerals
Tourmaline, Pyrite, Quartz,Feldspar, Sphalerite
SES4U
Unit: Earth Materials
More elongated
Stubby or
than equant,
blocky or
slightly longer
tabular
than wide, flat
Feldspar, Topaz
tablet shaped
Flat, tabletPlaty
shaped,
prominent
Wulfenite
pinnacoid
Tetrahedral
Tetrahedrashaped crystals
Tetrahedrite, Spinel, Magnetite
Aggregates
Wheat
resembling
sheaf
hand-reaped
wheat sheaves
Stilbite
SES4U
NAME OF TEST
Unit: Earth Materials
Mineral Identification Tests
How to Perform/ Complete
2-3 Example Test Results
SES4U
Unit: Earth Materials