Minerals

What the syllabus says you need to know - and the details...

1.1 Rock exposures are formed of minerals, rocks and fossils 

Minerals are naturally occurring elements or compounds with fixed properties - the one below is quartz.

Rocks are naturally occurring materials formed of minerals or fragments of rocks or fossils - The rock below is granite, made from the minerals quartz, feldspar and mica.

Fossils are any preserved sign of past life, more than 10,000 years old - this is a trilobite.

Ok - nothing but a few definitions - just need to learn these for 1 mark responses.

1.2 Minerals are formed in a number of geological environments...

Crystallisation from a melt [quartz, feldspar, mica] 

This is when the minerals were in a magma, so they were liquid rock, and the magma cooled. When it cooled it went solid and the crystals of minerals were made as this happened. An example would be feldspar - see below.

Metamorphic recrystallisation [calcite, garnet] 

The chemicals that made the minerals were in rocks as something else. When the rocks were metamorphosed by heat or pressure the minerals made new crystals and became new things. Garnet is made like this - see picture below.

Crystallisation from solution in evaporating water [halite]

This happens when the chemicals that are going to make the mineral are dissolved in warm water that goes on to evaporate in the open air. When the water evaporates the chemicals are left behind and form the crystals of the new mineral. The classic mineral formed in this way is halite - see below.

Crystallisation as cement from flowing pore waters [quartz, calcite]. 

Again- the chemicals that will make the mineral start dissolved in water. A typical example would be calcite (shown below) where the calcium carbonate is collected as water flows over or through limestone and is then deposited as the water flows through  the pores in another rock (like sandstone). This deposition into the pores in the rock make that rock get much stronger.

Crystallisation from hydrothermal fluids [in veins and faults; gangue minerals; quartz, calcite, ore minerals; haematite, galena]. 

This is similar to making minerals by evaporation. The chemicals will have been dissolved into hot water, normally when flowing near to an igneous intrusion. As the water cools, the minerals crystallise out from the fluid. The classic minerals for this are quartz, calcite, haematite and galena (shown below).

The minerals in sedimentary rocks have undergone sedimentary processes [rounding, sorting].

You need to know the gradation from angular (just eroded from the source rock) to rounded (been separate for a while suffering from travel and the weather). See below... (Thanks to Powers, 1953)

Minerals can be valuable if they contain metals [ores: haematite, galena, gold] or have properties such as being rare, hard, lustrous and/or coloured that cause them to become precious or semi-precious stones [for example quartz in the form of amethyst and, of course, diamond].

You're likely to be asked to explain how one or more of these mineral forming processes occurs - and to be able to give an example of a mineral made in that way.

So that's it: Everything you need factually on minerals. You'll also need to know how to do Moh's hardness test, a streak test, lustre checking, density testing and how to look for cleavage in a mineral. The links below might be useful...
Moh's hardness http://geology.about.com/od/scales/a/mohsscale.htm
Streak test http://www.gemsociety.org/wow/do2.htm
Lustre Useful Lustre site
Density testing Density of Minerals (Specific Gravity)
Mineral cleavage (you only need the first bit from)... Mineral Cleavage
These skills are likely to need to be applied to use in a flow chart style identification key.