416 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



The especially bright colors of some of the variscite from this locaUty 

 are rarely found in that from other places and the variety of markings 

 shown by the matrix is probably equal to any other material found. 



GENERAL DESCRIPTION. 



The material available for study consists of nodular aggi'egates of 

 variscite, irregular in shape and of various dimensions. The deep 

 green aggregates of crystallized mineral consist of tabular crystals, a 

 few of which reach a millimeter in length. Their breadth is about 

 half their length, and their thickness varies from about one-fourth of 

 a millimeter to very thin plates. The coarser aggregates of variscite 

 consist of well-developed crystals (shown in pi. 33, upper figure), 

 which are often nearly complete. The finer-grained material does 

 not show such distinct crystals, while the very fine-grained com- 

 pact mineral has more the appearance of a crypto-crystalline mass. 

 Several small cavities in the coarse material were lined with pro- 

 jecting crystals, which furnished good material for crystallographical 

 study. A view of such a cavity, enlarged six times, is shown in 

 plate 33, lower figure. The crystals are transparent and pale green 

 when viewed under the microscope. 



OPTICAL PROPERTIES. 



ORIENTATION AND PLEOCHROISM. 



The crystallographical orientation of the variscite crystals was so 

 chosen that the large flat face became the brachypinacoid 5 (010), 

 and the striations on this face were placed vertically. Variscite 

 being orthorhombic, these facts are sufficient to definitely orient the 

 crystals, so that the optical relations can be readily comprehended. 

 The basal pinacoid, c (001), was not observed on these crystals, and 

 the macropinacoid, a (100), is a rare form, seldom larger than a nar- 

 row face between the unit prisms m and m'" . 



The optical relations were ascertained by studying the flat crystals, 

 and also by means of two thin sections of the granular aggregate, 

 which were carefully prepared without being subjected to any heat. 

 If a section of the granular variscite be made in the ordinary manner, 

 it will be found that the heat employed in the operation is sufficient 

 to cause the green color of the mineral to change to the deep laven- 

 der, with consequent changes in the various physical properties of 

 the mineral. 



The extinction is parallel in all sections, and the mineral behaves 

 optically in strict concordance with the orthorhombic symmetry of 

 the crystals. 



The axial plane is parallel to the flat face h (010), the acute bisec- 

 trix is normal to the base c (001), the obtuse bisectrix then being 

 normal to a (100). The mineral is positive, so that the acute bisec- 



