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Posted in response to Looking for a Serpentine Expert - PA/MD from Fred Kelso on December 22, 2006 at 17:09:42:
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Hi Fred The Serpentine Group minerals can be the devil's own job to sort out - especially when you add the various forms of the species to the pot. Lizardite is one of the species of the Group, while "Williamsite" and "picrolite" are essentially forms of the species antigorite. The problem is, lizardite (and, to some extent, amesite) can also be found that qualify for the "williamsite" and "picrolite" tags. So it can take chemical and structural analysis to be really sure of what you have in hand. Your best bet for sorting out the *species* (singular or plural) you have is published information on the specific localities or geologic district your specimens come from. The more "learned" the publication providing the information, the more you can depend on it to be accurate. For example, a publication of the State's Geological Survey is more likely to have correct information than - say - an issue of a popular mineral magazine, such as Gems & Minerals. That all said, "picrolite" is the name given to (mostly) columnar antigorite. It looks sort of like a bunch of pencils banded together - but the cross sections of the columns won't be hexagonal, and may be rather irregular, no really fixed shape. The diam. of the columns is typically 1/8" or less - sometimes almost like a bunch of needles rather than pencils - but can be up to perhaps 1/4" across, maybe even a bit larger. At the lower end of the scale there is a grey area between "picrolite" and "asbestiform" antigorite. I personally feel that if the "needles" are stiff, they're "picrolitic" but if they are flexible they'er "asbestiform." "Williamsite" is basically a homogeneously massive form of antigorite - no "structural features" of any sort visible in it, except maybe random fracture lines. I'm not sure if there is an accepted color range, but the material I've seen has usually been on the pale, pastel, green side - not dark green. The darker shades of massive antigorite are usually what is referred to as "precious serpentine" - the stuff that can be used to make decorative items of a luscious deep green color. It is often used the same way the "jade" minerals are used. But, then, "williamsite" can also be used in such lapidary applications; it's just that the items will be lighter in color - as are a lot of "jade" items. So you once again find yourself in a grey area: Is it "williamsite"? Or "precious serpentine"? I don't know how much the above will help you. If it doesn't really answer your questions, you might give the Mindat.org eBB a try - where you can attach a photo to your query in the Identity Help forum. (If you want to post more than one photo, just "Reply" to your initial post, attaching the photos to your replies.) I guess I should also point out that a lot of the serpentine minerals that are found in the types of deposits you have samples from is just plain "antigorite" or "lizardite," or possibly "amesite." Just massive stuff that doesn't really qualify for any distinction beyond the species name. In fact, the vast majority of such depsoits are this way. Finds of "picrolite" and "williamsite" are uncommon - and finds of true "precious serpentine" are rather rare. So don't be surprised if the Mindat gang tells you that what you have is a plain old Serpentine Group mineral. Also, given the lack of distinguishing charateristics between some of the species, you may also find that it will take lab work to pin the species down - especially if you can't find published information which tells you what species are found at the localites you've visited. Good Luck! - I'm afraid you're gonna need it with the "pesky serpentines"! :~} Alan
From Alan - December 23, 2006 at 10:31:54
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