Minerals Physical Properties AS-A level Geology Minerals Physical Properties 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 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

Lustre The way in which minerals reflect light Vitreous, Metallic, Pearly, Silky or Dull

The mineral reflects light like glass Vitreous Lustre Halite The mineral reflects light like glass

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

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

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 cherry red streak

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 (7.5) Ore of lead and Haematite (5.5-6.5) Ore of Iron Most of the silicate minerals have relative densities between 2.5 and 3.2

Measured on Moh’s scale from 1.0 (softest) to 10 (hardest) 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

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

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

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

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

The way a mineral breaks when struck by a hammer 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

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

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)

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.

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

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

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

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

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