How can a mineral be seperated from a rock of which they are part.?

Answer 1

It depends on the mineral you are trying to concentrate or separate.
Let's put a common example. You want to concentrate Zircons and/or biotite from a granite.

First you have to ground your sample at a convenient size that will depend on the size of the crystals you want to separate. Keep in mind that the finer the grain, the harder to concentrate. So you want to keep your grain size as big as you can.

Then you seive the material and select a usually 0.5 or 1 mm or grains are OK to work with, but again it depends on the grain size of your rock.
For zircons you can go smaller.
Then you can use heavy liquids with a density of 3.0 gr/cc so lighter minerals like quartz, plagioclase, K-feldspar will float, and the heavy minerals like magnetite, pyroxenes, olivine, apatite, zircons will sink. Then you separate and clean these fractions.

Now you can use a Franz magnetic separator, which will separate minerals based on their magnetic properties. Magnetite you can concentrate with a magnet instead (it is more convenient). Zircons and apatites are not magnetic, but pyroxenes and biotites are. So you can effectively separate minerals with this method.
Then you can dissolve with acid apatite and other minerals and you end up with nice zircons. You have to check the up and hand-pick the crystals you want (with a brush under a binocular lens).
In the case of biotite, you can either try again the Magnetic Franz separator set at very precise conditions or try even nastier heavy liquids, or simply hand pick. or a combination of them. You can grind your crystals and repeat if necessary to improve the purity.

As you can image this is tedious, but it worth the effort to get a good date.

For zircons they are usually concentrated in a vibrating table with water, imitating the famous gold panning, but in this case is zircon panning that is better than gold for geologist.

Answer 2

It depends on the mineral and rock.

Very hard minerals could probably be frozen. If the mineral was pure enough, it would probably shrink ever so slightly. The rock, depending on its porosity, might have capilary water in it and actually expand some.

Another technique would be to heat the formation, like on a grill or in a fire. The mineral, depending on what it is, most likely has a much higher melting temperature than the rock.

If the mineral is hard enough, just hit the rock with a hammer to break it up.

Answer 3

The first step is usually to crush the rock into lumps using a device such as a cone crusher or jaw crusher.
The lumps are then milled to a powder either in a ball mill or rod mill depending on how hard the rock is and what size powder you want.
Milling frees all the minerals from the surrounding ones so the final powder is a mixture of grains of different minerals.
The next step is to separate out the grains of minerals you want to recover.
How this is done depends on the properties of the mineral, for example it may be magnetic so high power magnets could be used to extract it.

In practise most minerals are separated using froth flotation. This is like the magic bullet of the mineral separation world; its quick, cheap and unbelievably effective. Think of it as smart soap: it only washes out the mineral you want to wash out, and it works by exploiting differing surface properties of different minerals. Its invention over 100 years ago marked the point at which vast quantities of metals became cheaply available - with all the implications that had for society.

There are many other methods for separating minerals:
jiggers, vibrating tables, spiral gravity separators, electro-static separators, grease tables( for diamonds) and dense media separators to name but a few, but flotation remains by far the most versatile.

One last point on crushing. Grinding of rock to powder accounts for over 5% of global energy production - a vast amount by any standard, yet only 100th of that power actually goes into breaking the rock ! The rest is wasted has heat, friction and noise.
To make the process more efficient, microwave systems are now being investigated. These use heat to micro-fracture the rock making it much easier to crush.

Answer 4

It depends a lot on the physical and chemical properties of the mineral and surrounding rock. If the mineral is maleable, simple smashing of the surrounding rock might free it such as is often done with gold ore or the crushed rock might be soaked with a chemical that dissolves the gold and then is later recovered. The minerals can be pounded out with a pick and hammer as might be done with some jewels. Often the ores are heavier and they are put through sluices which trap the heaviest pieces.