Vermiculite from Mineral Hill, Elwyn, Middletown Township, Delaware County, Pennsylvania, USA
USA | |
| Joe Dunleavy (Pers. Comm.) |
Gordon's Mineralogy of Pennsylvania (1922) p. 191 | |
Gordon, S.G. (1922) The Mineralogy of Pennsylvania. Special Publication No.1, The Academy of Natural Sciences of Philadelphia, 255 pages, at p.191. |