Document x1rBpj4BwvJjpYVzLwM9GXMLm

FILE NAME: RT Vanderbilt (RTV) DATE: 1982 Aug 25 DOC#: RTV087 DOCUMENT DESCRIPTION: Letter from Univ of Maryland to Rollins Burdick Hunter of II. - Samples Sent are Identified as Tremolite Talc DEPARTMENT OF GEOLOGY 301- 454-3548 UN1-V ER S I T Y O F M'A R Y L A N D DIVISION F AGRICULTURE AND LUE SCIENCE* ' COLLEGE PARU 20742 August 25, 1982 Mr. George MacDonald RoJHns Burdick Hunter o f I l l in o is , Inc. 10 South Riverside Plaza Chicago, I llin o is 60606 Dear Mr. MacDonald; Using polarized lig h t microscopy and dispersion sta in in g , I have examined the sample you sent to me id e n tifie d as trem olitic. t a lc . I have id en tified the follow ing minerals In th is sample: p laty ta lc,- trem o lite, fibrous ta lc and anthophyl 1it e , Of these, trem olite and anthophyl1Ite can occur in nature In an asbe5tiform habit and are then c a lle d asbestos. The c h a ra c te ristic s of th is habit which are v is ib le using the o p tica l misroscope are: t , fib e r bundles exh ib itin g splayed ends Z . p a r a l l e l e x t i n c t i o n (The n O n - a s b e s t i f o r m v a r i e t i e s may e x h i b i t o b l i q u e e x tin ctio n .) 3- curved fib ers k. extreme elongation often in excess o f 100:1 * The trem olite and anthophyl11te present as major constituents of th is sample do not e x h ib it any o f these c h a r a c te r is tic s . A ll o f the trem olite and anthophyl1it e p a r tic le s I observed are properly calle d cleavage fragments. Most of the cleavage fragments are elongated and many have aspect ratios In excess o f 3:1. According to our e x is tin g federal government regulations these cleavage fragments can be calle d fib e r s . However, th is Is not m ineralogically v a lid . [ observed no anthophyl1it e or trem olite asbestos fib e rs in the sample I examined, There are, however, true mineral fib ers In the sample, I have id en tified them as fibrous t a l c . They are distinguished from the amphlboles .tremolIte and anthophyl1it e on the basis o f th e ir index o f re fra ctio n . The maximum index o f refractio n o f fibrous t a lc does not exceed 1.598. A ll o f the fibers I observed In th is sample had indices o f refractio n equal to or lass than 1.596. This value is much too low for trem olite or anthophyl1it e asbestos. Fibrous t a lc is thought to form from anthophyl1it e . It also e x h ib its the ch aracteristics lis te d above for the asbesfeiform h ab it. Although I did not observe any in the sample portion I examined, there may be a few fib e rs which- f a ll somewhere between anthophyl11te-asbestos and fibrous t a lc present from th is L ocality. The abundance o f thFs m aterial is vanishingly small and is should be considered as occuring in trace q u an tities only, - Sincerely yours, Ann G. Wylle Associate Professor WES000840