Mineral Properties
There are over 300 kinds of minerals on earth.
We won't go through all of them but we have highlighted some common rock building minerals as well as some common household ones here.
Common Rock Building Minerals
Scroll through to view. Description below.
How do you tell minerals apart?
As you can see from some of the above pictures, we cannot tell a mineral by just its colour. We can use the following to help us:
Colour and Luster
Colour can be used for identifying minerals but as you can see below, some minerals can exhibit different colours. This is not the best way to tell minerals apart, although some minerals can exhibit one colour (Olivine). Luster is better and can tell some minerals apart. Is the mineral glassy or opaque? Is it shiny/metalic or dull?
Calcite can come in many colours of the rainbow. it is usually dull in luster.
Quartz also can come in all the colours of the rainbow due to impurities. It is usually glassy in luster.
Hardness
Some minerals are harder than others. This can be a great way to tell them apart. A diamond, moissanite, quartz and cubic zirconia can all look the same to an untrained person. By testing the hardness you can tell which one it is. The standard is to use the Moh's hardness scale. It goes from 1(softest) to 10 (hardest). The scale is below.
Streak Test
Minerals all streak a particular colour when rubbed against a ceramic plate or sandpaper. Minerals that look like one colour may streak a completely different colour. This can indicate the type of mineral it is.
Although Gold in colour, this Pyrite streaks black.
Although pink in colour, this Calcite streaks white.
Cleavage and Fracture
If when broken a mineral comes apart randomly, it is called Fracture. If when broken it comes apart in angles and sheets, it is called Cleavage. Be careful though, when mineral crystals grow, it can be mistaken for cleavage.
Mica has 1 plane of cleavage and breaks into sheets.
Hematite fractures. As you can see, there are no flat surfaces
Quartz in crystal form has flat surfaces, but if you try to break it, it fractures. The rose Quartz at the right is representative. It is random. The far left is a polished smoky quartz. Quartz fractures, does not exhibit cleavage.
Other Properties
Some minerals with Iron are magnetic, or can attract a magnet
Some minerals can conduct electricity such as Copper and Peacock Ore (pictured).
Some minerals react with vinegar (acid) such as Calcite.
