EPA 2014c), was the site of a former mine that produced vermiculite contaminated with a mixture of asbestiform amphiboles, including winchite, richterite
, and tremolite asbestos (Meeker et al.
The studied volcanic outcrops are constituted by lamproites composed by forsteritic olivine, Ti phlogopite, diopside, enstatite, richterite
with Ti and K, leucite, and Fe-rich sanidine.
Geological Survey (USGS), which worked in conjunction with the EPA at the Libby site, 95 percent of the amphiboles from the samples were winchite and richterite
, neither of which has ever been classified as asbestos.
Much of the fibrous material, including winchite and richterite
, did not fall into the definition above, despite containing long, thin "asbestiform" mineral fibers.
However, at T > 950[degrees]C instead of layered hectorite a needle-like richterite
, Na[NaCa][[(Mg,[Fe.sup.2+]).sub.5]([Si.sub.8][O.sub.22])[(OH,F).sub.2], forms (29).
The hornblende-plagioclase thermometry actually consist of two reactions, the A thermometer uses the edenite-tremolite reaction (edenite + 4 quartz = tremolite + albite, in quartz rich rocks) and the B thermometer uses the edenita-richterite reaction (edenite + albite = richterite
+ anorthite) (Holland and Blundy, 1994).
Amphibole forms of asbestos are often divided into those with considerable commercial exploitation (amosite and crocidolite) and those that are encountered largely as intrusions into other mineral deposits (tremolite, actinolite, anthophyllite); thus, tremolite is found in many chrysotile ore beds, and an amphibole that has been variously labeled as tremolite, richterite
, or winchite is found in vermiculite ore from Libby, Montana.
A humbler but more surprising offering from Madagascar was richterite
, in sharp, complete, lustrous, opaque greenish black crystals to 4 cm, from a small prospect somewhere in Toliara Province, in the extreme south of the country.
Abdel-Rahman (2006) analysed amphiboles from analogous but a little younger (Cambrian) peralkaline granite in Egypt and found here also mainly arfvedsonite (as we in Socotra) together with richterite
which we did not found in our samples.
In contrast, Libby amphibole is a mixture of six amphiboles, mostly winchite (84%), richterite
(11%), and tremolite (6%), including prismatic crystals, acicular fragments, and bundles of fibrils approximately 100 nm to 1 [micro]m in diameter with lengths up to 20 [micro]m (Meeker et al.
The major component species are forsterite, phlogopite, diopside, richterite
, chromite and pyrite, and some of the lamproites of the Kimberley area also contain some very rare species, including priderite, jeppeite and wadeite (Grice and Boxer, 1990).
Libby amphibole asbestos was determined to be composed of tremolite, winchite, and richterite
(Meeker et al.