>I would imagine that the use of chalk is simply because of the sheer whiteness of the material.<

Very true fitz, and as with all colours (and none colours) there are also variations in 'whiteness'. I first became interested in calcium carbonate because it's the principal white pigment used in Japanese paintings and prints. Chinese paintings generally use white lead so it's quite an easy test, if you're not sure whether a painting or print is Chinese or Japanese, to run an ultraviolet lamp over the white pigment; if it fluoresces the chances are that it's calcium carbonate and therefore Japanese. I seem to recall that some washing detergents employ a similar (though probably chemically different) trick by introducing a slight blueing agent to make the wash look whiter.

I did actually take a small portable UV lamp out to Avebury once to see if the chalk on the eroded pathways at the top of the bank fluoresced at all; it was a bit of a failure because it was tipping down at the time and I was loathed to remove even a small piece of chalk for proper 'indoor' tests. The problem at Avebury is also that even the eroded paths are actually quite dirty and any sort of dirt or growth on the chalk is going to inhibit the fluorescing of the material.

I've walked along the paths of the Avebury banks on moonlit nights and they do appear quite white but that's probably due to them just being white and not to any fluorescing effect. I do find the possibility, though, that Avebury, Thornborough and Silbury may have fluoresced under certain conditions - if they did they would have appeared very, very magical indeed.

>Couple all of this with the chalk being the rock that yields the best quality flint, then we could be heading towards a sacred geology.<

Hit the nail on the head there fitz, and I'd go as far as to say that Avebury is where it is for that very reason.

Hi Fitz,
>>I would imagine that the use of chalk is simply because of the sheer whiteness of the material.
<<

It only stays white when exposed to the air for a shortish time, I'm in the E Yorks Wolds and any lumps of chalk in the garden surface as a very creamy colour and are only white when they are freshly split. They soon dull and if on damp ground are prone to going green. If ancient sites were chalk-faced for the pure white appearance, they will have had to be cleaned or maybe coated to preserve their appearance. Some of the larger round hilltop mounds here would have looked spectacular with a white covering. I've also often pondered about the earthworks that are serpent-like ridges just under the brows of some hills and their visual impact if they were white. Speaking of which, there's a 5-wide dyke system, that's 5 parallel humps and ditches that originally stretched from Market Weighton to Bridlington, they pass through the chalk uplands, what a sight they'd be if white.

>>Couple all of this with the chalk being the rock that yeilds the best quality flint, then we could be heading towards a sacred geology.<<

There are lots of flint tools found locally displayed in the Hull and East Riding Museum but the best quality ones, and the knapping is superb, weren't from E Yorks, they're from I think Suffolk or Norfolk < don't quote me, ask the museum!> There's an excellent Neolithic display there, apparrently, they have over 44,000 neolithic to BA artefacts. The replicas of the Folkton Drums are fascinating, don't know if they are a unique chalk artefact, the workmanship is superb and it seems they were made from local chalk.
http://antiquity.ac.uk/ProjGall/middleton/

Rune

>I would imagine that the use of chalk is simply because of the sheer whiteness of the material.

I presume that Silbury Hill is made of chalk because that's what the ground is.

Like the White Cliffs of Dover.

Hi Fitz,

There is no date for the Thornborough Henges yet.