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USA | |
| Mineralogy of Pennsylvania-1922 Samuel S. Gordon, pg. 221-222 |
| Gordon, 1922. Mineralogy of Pennsylvania |
| Mineralogy of Pennsylvania-1922 Samuel S. Gordon, pg. 229 |
| Gordon, S. G. (1922) The Mineralogy of Pennsylvania, Special Publication No. 1, The Academy of Natural Sciences of Philadelphia, p. 230. |
| Mineralogy of Pennsylvania-1922 Samuel S. Gordon, pg. 229 |
| Benge and Wherry, XIII, 1906, 92 |
| Samuel G. Gordon (1922) "Mineralogy of Pennsylvania" p. 225. |