What is the difference between mineral groups and series?

Question

It seems to me when reading about minerals, groups and series are spoken about interchangably in similar types of contexts. Is there a difference? If so, what?

Answer 1

Hi Asked,

Not at all the same! Mineral groups or classes are (extremely) broad chemical groupings -- for example, all the carbonates are a group, and all the silicates are a group, etc. These are very broad associations, and more descriptive than predictive of geology at a particular site.

Mineral series, on the other hand, are sets of minerals related in that they may be found (in nature) in continuous gradation between limiting extremes of chemical composition, with consequent continuous variation of physical properties (as may relate to a thermal gradient during crystallization across a site, for example). Commonly this occurs across a substitution of a monovalent cation with a different monovalent cation, or a divalent for a divalent, or both at once (in two compositional axes), or across multiple compositional axes. This may sound like a morass of possibilities, but series can only occur with substituting ions of comparable size, so as to not disrupt the lattice packing, and that cuts down the possibilities from infinite to quite finite.

Now that's in nature; if you deliberately wish to engineer physical, chemical, or electronic properties in your experimental material by straining the lattice, etc. then you have quite a large experimental space to explore. Not to mention, if you want to engineer a deliberately non-crystalline (glassy) phase, such as recently reported cobalt-vanadium zirconium alloys. And so on!

-- Cheers, -- Mr. d.