136 Dana and Penfield — Mineralogical Notes. 



Art. XX. — Mineralogical Notes; by Edward S. Dana and 

 Samuel L. Penfield. 



1. A large crystal of Hanksite. 



Some two years since Professor G. J. Brush placed in our 

 hands for examination a large crystal, or rather group of crys- 

 tals, of an anhydrous sulphate related to thenardite. The 

 specimen had been received by him from Professor J. S. New- 

 bern T , who stated that he had purchased it in California but 

 was unable to learn the exact locality from which it came. 

 The examination proved it to be probably hexagonal in crys- 

 talline form, and in composition to consist of sodium sulphate 

 and carbonate in the ratio of 4: 1. Feeling reluctant to attach 

 a new name to a mineral of which only one specimen was in 

 hand, and that from an unknown locality, we postponed the 

 publication of our results until some further facts should come 

 to light. The same mineral has now been re-discovered and 

 in specimens so satisfactory as to justify their receiving the 

 name Hanksite, given by Mr. Hidden. 



The specimen examined by us consisted of a low hexagonal 

 prism, measuring transversely 75 mm , and in a vertical direction 

 20 mm ; this prism is penetrated by several other similar tabular 

 crystals but in varying positions, so that no general law of 

 twinning can be given. The basal edges were irregularly 

 replaced by pyramidal planes. Apparently the form is hex- 

 agonal, the prism and pyramid both being present, and the 

 measured angles of the former showing very little variation 

 from the required 60°. The analogy of the artificial sulphates 

 of sodium and potassium suggested, however, that the form 

 might be really orthorhombic, and the hexagonal aspect due to 

 twinning. The optical examination made to settle the question 

 was not satisfactory because the crystal contained so much 

 mud as impurity as to be transparent only in spots. Some 

 points were found, however, which gave an obscure uniaxial 

 figure with negative double refraction ; but this question 

 might not be regarded as satisfactorily settled were it not for 

 the excellent results which Mr. Hidden's crystals have afforded. 

 The pyramidal plane spoken of was rough and rounded and 

 was only distinctly seen on part of the edges. The approxi- 

 mate angle (supplement) measured on the basal plane is 43°, 

 which, referred to the vertical axis assumed by Mr. Hidden, 

 gives a symbol f(4045) ; required 43° 8'. 



An analysis of the mineral gave (Penfield) the following- 

 results, which are almost identical with those of Mr. Mack- 

 intosh : 



