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GCSE Geology

GCSE Geology. The Physical Properties of Minerals. Click anywhere on the screen to move on. The Physical Properties Of Minerals. Colour. Not particularly useful as a diagnostic property Some minerals show a wide variety of colours

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GCSE Geology

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  1. GCSE Geology The Physical Properties of Minerals Click anywhere on the screen to move on.

  2. The Physical Properties Of Minerals

  3. Colour • Not particularly useful as a diagnostic property • Some minerals show a wide variety of colours • Quartz can be transparent, white, pink, brown, purple, yellow, orange and even black • Many minerals show very similar colours • Calcite, plagioclase feldspar and halite are commonly grey or white in colour

  4. Lustre The way in which minerals reflect light Glassy, Metallic, Pearly or Dull

  5. Glassy Lustre Halite The mineral reflects light like glassAlso known as vitreous lustre

  6. Metallic Lustre Galena Minerals reflect light like metals Metallic lustre often tarnishes to a dull lustre

  7. Pearly Lustre The lustre of a pearl or mother of pearl Shows clearly on the cleavage surfaces of biotite and muscovite mica Biotite Mica Muscovite Mica

  8. Streak The colour of a mineral’s powder Obtained by rubbing a mineral specimen on an unglazed white porcelain tile or streak plate Useful for identifying metallic ore minerals Silicates generally do not mark the tile and have no streak White minerals streaked on a white tile will have a white streak Any minerals harder than the streak plate (6) will scratch it Haematite gives a red-brown streak

  9. Relative Density* Relative to an equal volume of distilled water at 4 degrees centigrade. 1 litre = 1000g (1kg) 1 cubic centimetre = 1g Controlled by the atomic weight of the constituent atoms (chemical composition) and the packing (atomic structure) A useful property for identifying metallic ore minerals, these usually have relative densities over 5.0 and feel particularly dense when hefted in the hand For example Galena (7.4) Ore of lead and Haematite (5.5) Ore of Iron Most of the silicate minerals have relative densities between 2.5 and 3.2

  10. Hardness Measured on Moh’s scale from 1.0 (softest) to 10 (hardest) Scale was devised by measuring the amount of noise and powder produced from rubbing a mineral on a metal file Talc 1.0 Diamond 10.0

  11. Moh’s Scale of Hardness 10 Diamond 9 Corundum 8 Topaz 7 Quartz 6 Orthoclase Feldspar Note diamond is over 30 x harder than corundum

  12. Moh’s Scale of Hardness 5 Apatite 4 Fluorite 3 Calcite 2 Gypsum 1 Talc

  13. Moh’s Scale of Hardness Steel nail 5.5 Fingernail 2.5 Copper coin 3.5 Window glass 5.0 Everyday objects can be substituted for minerals on Moh’s scale

  14. Testing For Hardness Try to scratch mineral specimens with substances of known hardness If a mineral is not scratched by your fingernail, but is scratched by a copper coin then it will have a hardness of between 2.5 and 3.5 If a mineral cannot be scratched by steel it has a hardness of over 5.5 Gypsum is scratched by a fingernail, hardness <2.5

  15. Fracture* The way a mineral breaks when struck by a hammer The type of fracture is not controlled by any weaknesses in the atomic structure of the mineral

  16. Conchoidal Fracture* This type of fracture is the same as that shown by window glass A series of concentric curved lines can be seen on the fractured surface A diagnostic property of the mineral quartz 5mm Rose quartz showing conchoidal fracture

  17. Cleavage The way a mineral breaks when struck by a hammer Cleavage is controlled by lines of weakness in the atomic structure of the mineral Minerals can have 1, 2 or 3 planes of cleavage 1 plane, parallel or basal cleavage 2 planes of cleavage that intersect at a characteristic angle 3 planes (cubic, rhombohedral)

  18. Minerals showing one plane of cleavage 1cm Biotite Mica One plane of cleavage enables the mineral to part along parallel lines. It is like a ream of paper that can be separated into individual sheets.

  19. Minerals Showing 2 Sets of Cleavage Planes 1cm 1cm Plagioclase Feldspar Augite Feldspars – intersect at 90 degrees Augite – intersect at 90 degrees

  20. Minerals showing 3 sets of Cleavage Planes 1cm Produced by the intersection of three cleavage planes Cubic cleavage 3 planes intersect at 90 degrees e.g. halite Rhombohedral cleavage 3 planes intersect at 60/120 degrees e.g. calcite Halite 1cm Calcite

  21. Acid Reaction Use dilute hydrochloric acid to test for carbonates Calcite effervesces (fizzes) and gives off carbon dioxide gas Calcite reacting and giving off carbon dioxide 2cm

  22. Taste If a mineral can be tasted in the mouth, then it is soluble in fresh water Halite (rock salt) tastes salty and is a diagnostic property of the mineral

  23. Diagnostic Properties • Properties that allow any mineral to be identified • Most minerals have two or three diagnostic properties • Hardness, cleavage and streak are most useful • Colour, lustre and density are less useful • Special properties such as acid reaction or taste, are often used to identify a mineral • The properties marked with a * are not on the GCSE specification.

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