This document provides information on 20 different minerals. For each mineral, it gives the mineral name, key physical properties such as hardness, crystal structure, cleavage, color, and identifying characteristics. Pictures or diagrams are also provided to illustrate some mineral characteristics. The minerals discussed include common rock-forming silicates as well as oxides, sulfides, carbonates, halides, and sulfates. Key identification tests involving hardness tests, streak tests, cleavage, crystal habit, and other properties are summarized for each mineral.
2. Quartz (silicate)
Hardness 7, not
scratched by steel
No cleavage but shows
conchoidal fracture
Hexagonal crystals
terminated by pyramids
5mm
1cm
Quartz (variety citrine) Rose quartz showing conchoidal fracture
3. Orthoclase Feldspar (silicate)
Hardness 6, barely
scratched by steel
2 cleavages intersecting at
90° results in blocky shape
Commonly flesh coloured
Crystals show
simple twinning 2cm
4. Plagioclase Feldspar (silicate)
1cm Hardness 6, barely
scratched by steel
2 sets of cleavages
intersecting at 90°
resulting in blocky form
Commonly creamy
white or grey in colour
Crystals show multiple
or repeated twins
5. Biotite Mica (silicate)
Hardness 2.5-3.0
scratched by a
copper coin
Shows perfect
basal (parallel)
cleavage
Has a distinct
pearly lustre
Brown or black
in colour 2cm
6. Muscovite Mica (silicate)
Hardness 2.5-3.0
scratched by a
copper coin
Shows perfect basal
(parallel) cleavage
Has a distinct
pearly lustre
2cm
Whitish, straw or
silvery in colour
10. Andalusite/Chiastolite (silicate)
Hardness 6.5-7.5, not
scratched by steel
Occurs as needle-like
crystals but square in
cross-section
Crystals have dark
1cm inclusions in the centre,
like lead in a pencil
11. Garnet (silicate)
Hardness 6.5-7.5, not
scratched by steel
Rhombdodecahedral
crystal form, 12 faces
each one a rhombus
No cleavage
Red/brown or
green in colour
2cm
Almandine Garnet, Peru
12. Chlorite (silicate)
Hardness 2.0,
scratched by fingernail
Perfect basal
(parallel) cleavage
Greenish colour
Feels greasy when
rubbed between
the fingers
Alteration product
1cm from amphiboles,
pyroxenes and micas
Chlorite, Val Di Vizze, Italy
13. Calcite (carbonate)
Hardness 3, just scratched
by a copper coin
Perfect rhombohedral 1cm
cleavage, 3 planes
intersect at 60°/120° to
give cleavage rhombs
Effervesces and gives off
carbon dioxide when
dilute hydrochloric
acid is applied
14. Fluorite (halide)
Hardness 4, scratched
easily by steel but not
by a copper coin
Perfect octahedral
cleavage, cubic crystals
have the corners
missing at a 45° angle
Fluoresces in ultra
violet light
Commonly purple, green
or yellow in colour
1cm
15. Halite or Rock Salt (halide)
Hardness 2.0-2.5,
2cm
scratched by a
fingernail
Perfect cubic
cleavage, 3 planes
intersecting at 90°
Tastes salty when
put on the tongue
Halite, Neuhof, Germany
16. Gypsum (sulphate)
Hardness 1.5 -2.0, easily
scratched by a fingernail
Perfect basal
(parallel) cleavage
2cm
Often fibrous in
appearance (satin spar)
Arrow head/fish tail
twinned crystals common
17. Barytes/Barite (sulphate)
Hardness 3.0-3.5,
barely scratched by a
copper coin
Dense for a non-
metallic mineral (4.5)
Often shows perfect
basal (parallel)
cleavage, occasionally
displays 2 cleavages
Commonly shows
bladed crystal 2cm
18. Chalcopyrite (sulphide)
Hardness 4, not
scratched by a
copper coin
Black streak with
gold strands within it
Metallic lustre
Greenish gold colour
Tarnishes to
1cm peacock colours
19. Iron Pyrite/Pyrite (sulphide)
Greenish black streak
Hardness 6.0, barely
scratched with steel
Metallic lustre
Brassy gold colour
Cubic crystals show
striated faces
Strikes fire (sparks)
with steel 1cm
20. Galena (sulphide)
1cm
Perfect cubic
cleavage, 3 planes
intersect at 90°
Hardness 2.5, easily
scratched by a
copper coin
Lead grey streak
Very dense (7.5)
21. Haematite (oxide)
Hardness 5.5-6.5,
barely scratched by
steel
Cherry red streak
Metallic lustre
Often occurs as
kidney shaped masses
with a fibrous internal
structure 1cm