As promised here is the second episode of ANDYSEZs on cave mineralogy. It is likely that this will keep us all amused through as many episodes as "Blue Hills" - which eventually did come to an end, or "The Archers" which hasn't after more than fifty years. You may need to dig out ANDYSEZ 38 from the last ACKMA Journal to refresh your mind with some of the terms used below.

First of all - the plug! If you haven't already ordered it or worked out how to get it through inter-library loan or whatever lay your hands on the second edition of Carol Hill and Paolo Forti's Cave Minerals of the World (published by the National Speleological Society). This is the definitive cave minerals textbook with discussion on everything - with special chapters on various strange issues such as the colour of speleothems and the calcite/aragonite question. It costs about $US65.00 and is available through Speleobooks, for example (speleobooks@speleobooks.com). It is worth every penny or cent or whatever. It is profusely illustrated with diagrams, colour pictures and contains many references to original works. I must wrest my copy back from Yarrangobilly!

Whilst you are in a reading mood Trevor Shaw's History of Cave Science (published by the Sydney Speleological Society - get it from Ross Ellis, 18 Arkana Street, Telopea, NSW. 2117) has a very interesting chapter on speleothems and the evolution of ideas on their formation under such headings as:

• Formation by vegetative growth
• Formation by solidification of water
  • By an external petrifying power
  • By extreme cold
  • By extreme stillness
  • By unspecified causes
• Deposit from vapours
• The lapidifying juice
• Deposit from suspension or solution
• Deposit from water containing carbon dioxide.

Trevor's chapter concentrates mainly on carbonate and gypsum speleothems. I particularly like the term "lapidifying juice"! Out with the OED! Lapidify: Make into stone.

The very next entry in the Concise OED happens to be Lapis lazuli: A sodium aluminium silicate containing combined sulphur, blue pigment from it, its colour. As far as I know lapis lazuli (also known as lazurite) doesn't occur in caves although my trusty Rutley's Elements of Mineralogy states that it occurs "in crystalline limestone near granite contacts...". I must have a look next time I am at Yarrangobilly or Cooleman!

But it is a mineral made up of three metals (sodium, aluminium, silicon), the non-metallic element sulphur and the gas oxygen. But it may be more complicated yet! Rutley describes lazurite as sodium aluminium silicate with sodium sulphide. The chemical formula is:

3(NaAlSiO4).Na2S

This means that there are three lots of sodium, aluminium and silicate ions - the last ion is made up of one atom of silicon and four of oxygen, together with the sodium sulphide (count the atoms and ions in this for yourselves - there will be a small prize for the first correct entry). Note the "dot" after the bracket. This means that the crystal lattice is made up of essentially the two entities on either side of the "dot". The colour of the mineral is probably due to the sodium sulphide. However, this doesn't have much to do with caves.

Whilst I am wittering on about irrelevancies why do we keep finding mineral names ending in the suffix "-ite"? Again the trusty OED is brought to bear. -ite: belonging to or connected with. For example, calcite - a mineral with connections to calcium.

In the future ANDYSEZs we will get to more detail on cave minerals starting with the carbonate minerals that are chiefly calcium or magnesium based but iron carbonates are also commonly found. Many other carbonate cave minerals are known but are not usually products of karst processes.

From the carbonate group we will go on to examine the sulphates, halides, phosphates, nitrates, oxides and hydroxides and so on - ad infinitum! Minerals related to metal ores can also be locally important as can those related to organic compounds.

One thing we are not going to do is to get into classical crystallography! As taught 35 years ago (and, I am told, since then) it can be a subject of mind-numbing banality. I am sure it can be made interesting and highly relevant but I was so turned off by such things as interfacial angles, planes of symmetry and the Laws of Rational Indices that I couldn't face trying to learn it to re-broadcast it to you. I suppose you should know that calcite belongs to the:

Hexagonal system - Axes, a, a, a, c, three equal horizontal, making angles of 120° with each other, a vertical axis at right angles to the plane containing the horizontal axes. Calcite type - symmetry: - 3 planes, 4 axes (3II, 1III), a centre.

Enough!

We will have a little rest from minerals next time. Unless someone comes up with a really interesting questions we will talk about the surface area of an egg carton. Makes a change from snail-wrangling.