SGM 210: GEOMATERIALS AND PROCESSES

Practical: Minerals

… is a naturally occurring, solid, with highly

ordered atomic arrangement, homogeneous chemical composition.

Minerals are formed by inorganic processes

Mineral…….

Identifying minerals

Physical Properties

COLOUR :Not always reliable!!! Be careful STREAK LUSTRE : metallic, vitreous

Physical Properties

TRANSPARENCY: translucent, opaque FORM OR SHAPE: euhedral, anhedral

Physical Properties

HABIT: fibrous, needle-like, tabular CLEAVAGE:

TENACITY: brittle, malleable

Physical Properties

SPECIFIC GRAVITY : the ratio of weight of a stone to that of an equal volume of water.Some Common Minerals and Their Specific Gravity

Halite (2.1)

Gypsum (2.3)

Quartz (2.7)

Talc (2.8)

Physical Properties

HARDNESS

Magnetism Radioactivity Solubility in acids Sensory tests “odour, taste or feel”

Other diagnostic properties

Silicates(most abundant): all contain the (Si)

and (O) anions Carbonates : al contain the (CO3)2- anion

Sulphates : all contain the (SO4)2-

Halides : all contain at least 1 halogen anion (F-,CL-, Br-, I-)

Oxides : all contain at least O2- anion Sulphides :all contain an S2- anion Phosphates: all contain the (PO4)-3

Most Common Groups

Olivine group Garnet group Aluminosilicate group Humite group Phenacite

Nesosilicates

Group Nesosilicates

Colour Yellowish green, olive green, greenish black or reddish brown

Hardness 6.5-7

Streak White

Lustre Vitreous

System Orthorhombic

End members Forsterite (Fe2SiO4)Fayalite (Mg2SiO4)Monticellite(CaMg SiO4)Kirschsteinite (CaFeSi04)

Olivine

Group

Colour Variable with composition

Hardness 6.5-7.5

Streak White

Lustre Vitreous to resinious

Crystal System Isometric

End members Pyrope , Almandine, Spessartine, Andradite, Grossular, Uvarovite, Hydrogrossular

Garnet Group (Mg2+ ,Fe2+ ,Mn2+,)3Al2Si3O12 – Ca3(Fe3+Al3+ ,Cr3+ )2Si3O12

Aluminosilicate (Al2SiO5)

Pyroxene group Amphibole group Pyroxenoid group

Inosilicates group

Group Inosilicates

Colour Black

Hardness 7.5-6.5

Streak Black

Lustre Glassy or metallic

System Orthorhombic or monoclinic

End members Enstatite, Ferrosilite, Diopside,hedenbergite

Cleavage 2 planes that meet at 90 degree

Pyroxene(XYZ2O6)X= Na+, Ca2+,Mn2+,Fe2+,Mg2+ and Li+

Y= Mn2+,Fe2+Fe3+,Cr3+ and Ti4+

Z= Si4+ and Al3+

Anthophyllite Cummingtonite series Tremolite series Sodium amphibole Group

Amphiboles

Mica group Serpentine group Chlorite group Clay mineral group

Phyllosilicates

Group Mica

Colour Black or brown to red

Hardness 2.5-3

Streak White

Lustre Vitreous

Cleavage Perfect cleavage in one direction

Biotite

Group Clay

Colour Usually white but other colours are known

Hardness 2

Lustre Dull earthy

Crystal system Triclinic

Kaolinite

Group Mica

Colour Silver-white sheen

Hardness 2.5-4

Streak White

Lustre Pearly, vitreous

Cleavage Perfect cleavage

Muscovite

Feldspar Group

K-feldspar Plagioclase feldspar series

Feldspathoid group Scapolite

Tectosilicates

Plagioclase

Alkali feldspar

Microcline Sanidine

Orthoclase

Alkali feldspar

Group Silicate

Colour Variety of colors

Hardness 7

Specific gravity 2.66

Streak White

Lustre Vitreous

Crystal system Hexagonal

Quartz(SiO2)

Calcite Magnisite Siderite Rhodochrosite Smithosonite Aragonite Dolomite

Carbonates

Group Carbonates

Colour Variety of colors

Hardness 3

Streak white, grey

Lustre Vitreous , pearly

Calcite (CaCo3)

Group Carbonates

Colour Colourless, white or brown

Hardness 3.5-4

Streak White

Lustre Pearly, vitreous

Crystal System trigonal

Dolomite CaMg(CO3)2

Hematite group

Hematite Corundum Ileminte

Spinel group Magnetite Chromite Gahnite Spinel

Oxides

Hematite

Group Hematite Group

Colour Red to reddish brown

Hardness 5-6

Streak Red to brownish red

Lustre Metallic, submetallic

Crystal System Hexagonal

Magnetite (Fe2+Fe3+2O4

)Group Spinel

Colour Black to metallic silver grey

Hardness 5.5-6.5

Streak black

Lustre Metallic, dull

Crystal System Cubic