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USA | |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 108. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Maryland Geological Survey, Vol. VIII (1909): 107. |
| Gems and Minerals of America- Jay Ellis Ransom-1974 |
| Maryland Geological Survey, Vol. VIII (1909): 108. |