[DoctorBeaver (OP)]

OK I think I just about know what a rock is; but I'm not sure about minerals. What actually are they?

Q2) What would diamond be classed as?

[JimBob]

A mineral is defined in two ways.

1.) It has a specific range of chemical components (a solid solution.)
2.) There is a definition of the mineral's  crystalline structure.

For example: The olivine discussion in the thread http://www.thenakedscientists.com/forum/index.php?topic=13028.msg159103#msg159103

The solid solution diagram shows the possible variations in chemical compositions of olivine (in the green area, below) that will produce the same crystal structure and x-ray defraction pattern.



At the apex of this diagram is the gem peridot.

A diamond is a mineral. It is a solid, stable form of carbon as you are no doubt aware. The different colors found in diamond are produced by the inclusion of other ions in the crystal lattice, different heating histories and/or by the amount of radiation and electron excitation and alteration of the carbon atoms within the crystal. The deep greens, reds and orange colors of fancy stones can be artificially produced in clear stones by exposure to high amounts of radiation and heat. These are almost indistinguishable form naturally occurring fancy diamonds.

Rubys, on the other hand, are the mineral corundum. Corundum is also the gem sapphire. Their red color is produced by the addition of small amounts of chrome, blue color by titanium include in the crystal structure.

Emeralds are actually just the mineral beryl, a blue-green to yellow mineral normally, colored green by trace amounts of chromium and sometimes vanadium.

[DoctorBeaver (OP)]

Thank you, Jim.

1 other question - what are the 10, 40 & 90 on the right? Are they the level of solution of something?

[JimBob]

They are the percentages of the endpoints of the solid solution or the phases, whatever you wish to call the variation within this specific set of chemicals.

[DoctorBeaver (OP)]

Right, got it. Thanks again.

[another_someone]

I would have simply regarded a mineral as that which is mined (or could be mined).

Ofcourse, I suppose you could mine some extremophile bacteria, but until recently this was not considered a possibility (back to the issue of exceptions).

[DoctorBeaver (OP)]

I would have simply regarded a mineral as that which is mined (or could be mined).

Coal? Or what about ores?

[JimBob]

Coal is a compound, ores are a variety of minerals, compounds, and also elements disseminated within a larger body of rock. Gold occurs as inclusions in quartz, etc.

[DoctorBeaver (OP)]

I think I'll stick to particle physics & QM. I can understand a bit about them  []

[JimBob]

Well since I know little of either of the above - you can have them.