1. Physical Properties of Minerals

2. Colour and Streak One mineral can have different colours
Colours are therefore not always diagnostic for minerals
Minerals with metallic luster have less colour variations
than minerals with non-metallic luster
Streak = colour of fine powder can be different from crystal colour,
Tested with unglazed porcelain plate (hardness = 7)

3. Luster Metallic Non-metallic
Appearance of a mineral surface which reflects light
Non-metallic
Metallic
Vitreous
Resinous
Pearly
Greasy
Silky
Adamantine

4. Metallic luster
Metallic luster in pyrite

5. Vitreous luster = broken glass
Vitreous luster in quartz
Vitreous luster = broken glass

6. Resinous luster = piece of resin
Resinous luster in sphalerite

7. Pearly luster
= like a pearl
Pearly luster in talc

8. Greasy luster = thin layer of oil

9. Silky luster = looks like silk
Silky luster in chrysotile, a type of asbestoes

10. Adamantine luster
= reflectance of
light from a diamond

11. Other properties depending on light
Transparent = transmitting light
Translucent = transmitting light diffusely
Opaque = impermeable regarding light
Fluorescence = emission of light
during exposure with UV-light or X-rays
(f) Phosphorescence = emission of light
after the exposure with UV-light or X-rays

12. Transparent

13. Translucent

14. Opaque

15. Fluorescence

16. Minerals
in form
of aggregates

17. Parting and Fracture
Parting = breaking along planes of structural weakness,
produced by pressure, twinning, or exsolution
Fracture: the way minerals break which do not have cleavage or parting
Conchoidal: smooth curved fracture (interior of a shell)
Fibrous: after fibers
Hackly: jagged fractures with sharp edges
Uneven or irregular: rough and irregular faces

18. Cleavage Tendency of minerals to break parallel to atomic planes
Octahedral
Cubic
Dodecahedral
(12)
Prismatic
Basal
Rhombohedral

19. Hardness Fingernail: 2.2 Copper penny: 3.2 Pocket knife: 5.1
..the resistance that a smooth surface of a mineral offers to scratching
Fingernail: 2.2
Copper penny: 3.2
Pocket knife: 5.1
Glass plate: 5.5
Steel file: 6.5
Porcelain plate: 7.0

22. Specific Gravity ..or relative density expressed the ratio
between the weight of a material versus
the weight of an equal volume water at 4ºC
(density = 1g/cm3 in cgs units)
The denser the structure and the higher
the number of heavy elements,
the higher the relative density
e.g. test for gold vs gold-coloured minerals

23. But g/cm3 are not SI units!
The SI units for density, as opposed to specific gravity which is a unitless ratio, are:
kg/m3
So, converting from g/cm3 to kg/m3 ,

24. So, for example, water at 4ºC has a density of 1
So, for example, water at 4ºC has a density of g/cm3 , but in SI units the density is 1000 kg/m3 !
Specific gravity is numerically equal to density only in cgs units, but since it is a ratio, S.G. does not have units.

25. Magnetism, Radioactivity, Solubility and Piezoelectricity
Ferromagnetic minerals: possesses magnetic order;
attracted strongly.to a mganetic field (hand magnet);
Paramagnetic minerals: attracted to a magnetic field
Diamagnetic minerals: do not response to magnetic field
Radioactivity: decay of radioactive isotopes
(Geiger counter)
Solubility-test with HCl:
proof of CO3-containing minerals (fizz test= release of CO2)
Piezoelectricity: Generation of an electric current
in a crystal through directed pressure

26. Physical Optics Effects
Colour based on dispersion
So-called “fire”, which can be seen in diamond, zircon, rutile and some
amethyst, is caused by significantly differing refractive indice in the
mineral producing different absorptions of wavelength of light; e.g. red and
blue in amethyst.

27. Pleochroism – Dispersion caused absorption (absorption pleochrism) or
reflection (reflection pleochroism) of different wavelengths of light in
different orientations of a mineral.
Reflection pleochroism in covellite

28. Colour based on scattering
Chatoyancy – Refers to the appearance of a cat’s eye (from French
oeil de chat), which is caused by scattering of light in bands
perpendicular to the fibrous structure present in some minerals; e.g. satin spar, a variety of gypsum. It is also seen in the gemstones tiger eye and cat’s eye.
Polished tiger eye, in which the fibres are asbestos which have been
silicified ;i.e. permeated by quartz.

29. Asterism – Scattering yields three-pronged or six-pronged star patterns
caused inclusion in some minerals with hexagonal symmetry. This is
particularly impressive in the gem varieties of corundum, star rubies and
star sapphires.
Star sapphire

30. Aventurescence – Scattering produced by numerous small inclusions as
seen in aventurine quartz. In this case, the effect is produced by platy
Inclusions of the mica,fuchsite, and hematite.

31. Opalescence – Scattering caused by atom-sized structures that comprise the
mineral as seen in pearls and opal.
Precious opal in rock matrix

32. Colour based on interference
Iridescence – Colour produced by thin films such as tarnish. This can be produced on bornite, chalcopyrite or pyrite
Iridescent goethite

33. Colour based on diffraction
Labradorescence and Schiller – Diffraction gratings are produced by
periodic lamellar structure. In labradorite (Ca-rich plagioclase),
exsolution lamellae at low temperatures produced this effect.