In sci.geo.geology, on Tue, 14 Mar 2006 11:54:18 +0100,
Carsten Troelsgaard sez:

I missed this earlier..

` General info on flint and chert
` http://www.abdn.ac.uk/geospatial/sum...factsheet1.htm

` Quote
` Cryptocrystalline Quartz

` Cryptocrystalline quartz is simply quartz whose crystals are so small that
` they can only be seen with the aid of a high-power microscope. It is formed
` geologically from silica that has dissolved from silicate materials. Over
` geological time, this amorphous silica gel dehydrates to form microscopic
` crystals and eventually becomes what we know physically as rock.
` Cryptocrystalline quartz occurs in many varieties. These varieties have been
` named based on their color, opacity, banding and other observable physical
` features. Technically speaking, the two varieties that account for the vast
` majority of "flint" artifact materials are chalcedony and chert.

` Other varieties encountered in the artifact world are agate, jasper and
` petrified wood. Interestingly, petrified wood is usually wood that has becn
` replaced by agate. This same process also occurs with coral, hence the term
` "agatized coral".

` Chalcedony Chert and Flint

` Chalcedony is a variety of cryptocrystalline quartz with extremely small
` crystals and a specific gravity (weight under water, a measure of a
` rock/mineral's purity) nearly identical to that of pure quartz. Due to its
` very high quartz content and super fine particle matrix, chalcedony has a
` very waxy luster.

Yipes, what a horrendously mangled misdefinition of specific gravity.
By that definition, water has a specific gravity of 0, and wood has
a negative sg. I guess it's a mistranslation of something from another
language, intended to be read as "weight divided by weight of an equal
volume of water", at least I hope that's the explanation.


--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.