CHAPTER 1: MINERALS:
DEFINITION, PROPERTIES
AND OCCURRENCES
Sarah Lambart
CONTENT OF CHAPTER 1
„ Goal:
learn how to describe and classify minerals
„ 3
elements of classification: chemistry, structure and
environment
„ Outline:
„ Occurrences
of minerals
„ Classification
of minerals
„ Physical
properties of minerals
„ Definitions:
„ A
mineral is always (1) inorganic, (2) naturally
occurring, (3) with a structure and a composition
that give it defined macroscopic properties. A
mineral is most of the time a (1) crystal and (2) a
solid.
„ A
crystal is a homogeneous chemical compound
with a regular and periodic arrangement of atoms.
These arrangements present symmetries. A crystal is
not always a mineral. It can be synthetic or organic
(e.g., proteins)
MINERAL OCCURRENCES AND ENVIRONMENTS
Igneous
Half dome, Yosemite
(granite)
Sedimentary
Montaña de Oro State Beach
(shales)
Metamorphic
Sequoia National Forest California
(marble, schist and gneiss)
COMMON MINERALS &
MINERAL ASSOCIATIONS
„ Metamorphic
„ Omphacite
„ Jadeite
(amphibole)
(pyroxene)
„ Epidote,
chlorite
„ Sedimentary
„ Carbonates
„ Salts
(calcite, dolomite,…)
(halite)
„ Gypsum
„ Igneous:
„ Olivine
+ pyroxenes
„ Plagioclases
+ pyroxenes
ADDITIONAL SLIDE
„ Minerals
in igneous rock
Acid (SiO2>63 wt.
%) Rhyolite, granite Rock names
(intrusive, extrusive) Common minerals Quartz, alkali
feldspar
(plagioclase,
hornblende,
micas) Intermediate
(52<SiO2<63 wt. %) Andesite, dacite,
diorite, tonalite, Sodic plagioclase
(hornblende,
biotite, quartz,
pyroxene). Basic (45<SiO2<52
wt. %) Basalt, gabbro,
pyroxenites pyroxene,
plagioclase,
(Olivine, iron oxide,
titanium oxide,
quartz, amphibole,
micas) Ultrabasic
(SiO2<45 wt. %) Peridotite,
kimberlite Olivine,
pyroxene
(plagioclase
garnet,
amphibole,
spinel, micas) ADDITIONAL SLIDE
„ Minerals
in sedimentary rocks
„ Clastic
sedimentary rocks
„
Conglomerates and breccias (>2mm)
„
Sandstones (0.06-2mm)
„
Mudrocks (<0.06mm)
„ Chemical
sedimentary rocks
„
Siliceous rocks (silex)
„
Evaporite
„
Limestone, dolostone
„ Organic
„
sedimentary rocks
Carbonate rocks (guano, coal)
quartz, gold,
diamond,
apatite, calcite,
and clays
calcite, gypsum,
anhydrite, halite
and sylvite,
borate minerals
phosphates,
graphite,
calcite, fossils
ADDITIONAL SLIDE
„ Minerals
in metamorphic rocks
Basic rock
(basalt, gabbro)
Metabasite
Amphiboles
+epidote for LMG
+plagioclase for HMG
Clay-rich sedimentary rock
(shale, mudstone)
Metapelite
Muscovite + Quartz
+chlorite, biotite
garnet for LMG
+sillimanite, opx,
cordierite for HMG
Limestone
Marble
Calcite or dolomite
+micas, quartz, clay,
pyrite
CLASSIFICATION AND NAMING
„ >4000
mineral species
„ Classification:
based on the dominant anion
Sulfates: with SO42-
„
Gypsum (CaSO4 2H2O).
„
Oxide: Cation +
oxygen
hematite (Fe2O3)
Ex.: magnetite (Fe3O4)
„
Phosphates: with PO43-,
(or AsO43-,VO43-)
Apatite Ca5(PO4)3(OH)
„
Hydroxides: with OH-
Brucite Mg(OH)2
Ex.: gibbsite Al(OH)3
„
Borates: with BO32- (or
BO45-)
Borax Na2BIII2BIV2O5(OH)4 8H2O
„
Carbonates & nitrates :
with CO32- (or NO3-)
Calcite CaCO3
Ex.: Nitratite NaNO3
„
Native: no anion
Gold (Au)
„
Sulfide: with S2-, (or
As, Te)
pyrite(FeS2)
Ex.: Pt, Ag, Cu,
Ex.: galena (PbS2),
C(graphite or diamond) sphalerite (ZnS)
„
Silicates: with SiO44-
„
Halides: contained
halogens (F, Cl, Br, I)
“table-salt”(NaCl)
Ex.: Fluorite (CaF2)
SILICATES
„
Orthosilicates
Olivine (Fe,Mg)2SiO4
Ex.: pyrope Mg3Al2Si3O12
„
Chain silicates
Amphibole
„
„
Sorosilicates
Epidote Ca2Al2FeO(OH)SiO4 Si2O7
„
Sheet silicates
Muscovite
Cyclosilicates
Tourmaline
„
Framework silicates
(or tectosilicates)
Quartz SiO2
Ex.: Feldspar NaAlSi3O8
DIAGNOSTIC PROPERTIES
-
Habit
-
Morphology
-
Transparency
-
Luster
-
Color
-
Streak
-
Tenacity
-
Cleavage and fractures
-
Density
-
Hardness
-
Others
PHYSICAL PROPERTIES
„ Habit
Euhedral
„
Subhedral
Anhedral
Tabular/platy
Prismatic, acidular, fibrous
Morphologies:
Granular
„ Transparency
Transparent
(quartz)
Translucent
(garnet)
opaque
(lapis-lazuli)
„ Luster
Metallic
(pyrite)
Submetallic
(rutile)
Adamantine
(diamond)
Resinous
(amber)
Vitreous
(amethyst quartz)
Earthy
(desert flower)
ADDITIONAL SLIDE
„ Luster
examples
„ Color
Smithsonian collection (D.C.)
„ Tenacity
„ Streak
Credits: http://
depthome.brooklyn.cuny.edu/
geology/core332/minerals.htm
the ability of a mineral to deform plastically under
stress: Brittle > Sectile > Ductile
„ Definition:
„ Cleavage
„
Fracture
Definition: Cleavage = plane of weakness.
Conchoidal fractures
(obsidian)
„ Density
(or specific gravity)
Most silicates have a density between 2.6 and 3.5 g/cm3
„ Hardness
„ Mohs
scale
Moh’s scale
1
Talc
2
Gypsum
3
Calcite
4
Fluorite
5
Apatite
6
Orthoclase
7
Quartz
8
Topaz
9
Corundum
10
Diamond
Fingernail: 2.5
Copper penny: 3
Window glass: 5.5
Steel nail: 6.5
„ Other
properties
„ Taste
„ Magnetism:
(MnO2)
„ Acid-test:
magnetite (Fe3O4)> ilmenite (FeTiO3) > pyrolusite
Calcite
„ Fluorescence
(Fluorite (CaF2), calcite (CaCO3), nepheline)
„ Radioactivity
(uraninite (UO2), thorite (ThSiO4), carnotite)
„ Pleochroism
„ Electrical
conductivity