690 SCIENTIFIC RECORD FOR 1885. 



The author also discusses at length the optical coustaiits ot tlui s])e- 

 cies. Two plates of figures show the various habits of the ci ystals. 

 Some of the tabular forms are strikingly like the crystals recently ob- 

 tained in some abundance at Franklin Furnace, New Jersey (variety 

 fowlerite). 



Penfield has described crystals of tiemaunite from Utah and also 

 crystals of metacinnabarite from California. The former mineral, the 

 pure selenide of mercury, has hitherto been known only in massive form. 

 Itis now shown to crystallize in tetrahedral crystals, similar to sphalerite 

 in habit and in twinning. Metacinnabarite, the black amorphous sul- 

 phide of mercury described by G. E. Moore, is also shown to crystallize 

 in similar tetrahedral forms, the crystals, however, being less distinct 

 and perfect than those of tiemannite. These two species thus take 

 their proper places in mineralogical classification. It does not appear, 

 however, that the dimorphous forms of the sulphides of zinc and mer- 

 cury, wurtzite and cinnabar, bear any close relation to each other. 

 Penfield's determinations give the crystallized tiemannite a specific 

 gravity of 8-19, much higher than that before accepted for the species; 

 also that of metacinnabarite 7*81, while the intermediate compound 

 onofrite — the sulpho-selenide of mercury — from Utah lies between them 

 with a specific gravity of 8-04. 



Crystals of azurite from the Clifton mines in Arizona have been 

 measured by O. W. Huntington. They are shown to be highly modi- 

 fied, though not adding to the already large list of the species (this 

 list includes fifty-one or fifty-two planes). The measured angles also 

 correspond closely to those of the Chessy crystals. The Avork on the 

 descloizite crystals of Nev/ Mexico by vom Eath, according to whom 

 they are to be taken as orthorhombic, is referred to on a later page. 



The apparent cleavage of titanite parallel to the hemipyramid ?j (2 P 

 of the usually accepted form), conspicuous on the crystals from Northern 

 New York, has been shown by G. H. Williams to be only a structural 

 " parting," due to the interposition of twin lamellsB. It thus has the 

 same explanation as the frequently observed "cleavage," i)arallel to the 

 basal plane of pyroxene, and similarly in other cases. The same author 

 has described crystals of amphibole from Saint Lawrence County, New 

 York, which were interesting in showing several new planes in the 

 prismatic zone. Penfield has figured and examined optically some 

 curious composite crystals of analcite from the Lake Superior copper 

 region, remarkable for their symmetrical arrangement. The quartz 

 crystals of North Carolina, hardly second to those of the Alps in inter- 

 est and complexity of crystalline form, have received the attention they 

 deserv^e at the hands of vom Kath. His memoir upon them is accom- 

 'lianied by numerous figures showing the various types of forms. 



Additional observations on the crystalline form of the beautiful new 

 borate, colemanite (see the report for 1884), have been published by 

 Jackson, Hiortdahl and Arzruni. Palla has studied crystals of gothite 



