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Volume 7, pages 23-24, 1922

     EAKLEITE FROM ISLE ROYALE, MICHIGAN1 

WILLIAM F. FOSHAG AND ESPER S. LARSEN, Washington, D. C.

      A specimen labeled "Wollastonite, Isle Royale, Mich." in the United States National Museum was recently noticed to have the general appearance of the eakleite from the original locality at St. Inez, California, and further study has confirmed the suspicion that the mineral actually is eakleite.

      The specimen consists of an aggregation of radiating fibers, with a somewhat silky luster and a pale pink color. The material is exceedingly tough. Microscopic examination showed that it is made up mostly of eakleite, with properties similar to those of the mineral from California. The Isle Royale mineral is finer fibered and is less pure, as it contains several per cent of a weakly birefracting material that is probably a sort of serpentine or chlorite. This foreign material forms nests of small grains in the fibrous masses. The optical properties of this eakleite, compared with those of the original material from California, are:

Locality Isle Royale St. Inez 
 α  1.579±0.005 1.583
 β   1.583
 γ  1.590±0.005 1.593
Extinction Z||elongation Z||elongation
Optical character + +
Axial angle small very small

      The material for analysis was not entirely free from the chloritic admixture, but was of sufficient purity to indicate the nature of the mineral. The analysis, made by standard methods, is given below, together with the analysis of the original material from California; for comparison.

Locality Isle Royale St. Inez
SiO2 50.88 50.17
Fe2O3  1.32  1.04
CaO 42.88 45.45
MgO  1.10 tr.
Na2O  0.55 none
H2O(+)  0.12  
H2O(-)  3.68 3.18
  100.53 99.84

     

      The optical properties distinguish this mineral from wollastonite and indicate that it is actually eakleite, and the chemical analyses of the two occurrences are sufficiently close, to definitely confirm its assignment to that species. The great toughness of the eakleite from both localities is noteworthy. Dana gives as a locality for wollastonite the Cliff Mine, Keweenaw Point, and Isle Royale, Michigan, and describes the mineral as a very tough variety, having a red color. It seems evident that what is referred to is the eakleite described above. Dana notes the locality to be exhausted, but specimens will probably be found among the wollastonites in old collections.

 NOTE

      1 Published with the permission of the Secretary of the Smithsonian Institution and the Director of the United States Geological Survey.

The name Xonotlite has priority - DVB (see "The identity of eakleite and xonotlite" E. Larsen  American Mineralogist 1923) 

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