182 T. L. Walker — Examination of Triclinic Minerals. 



and are similar to those on 100 (fig. 11), thus indicating that 

 the mineral is centro-symmetric triclinic. 



Chalcanthite, or Copper Vitriol. — This triclinic mineral 

 rarely occurs in well developed crystals, so that the crystals 

 etched were artificial and grown from a saturated solution of 

 copper sulphate. About twenty grams of ordinary " blue 

 stone " was dissolved in hot water to concentration, acidified 

 with a few drops of sulphuric acid, filtered and allowed to 

 cool, when the larger portion crystallized out. The solution 

 was poured into a second dish and after twenty-four hours half 

 a dozen well-formed crystals had separated. These were used 

 for examination. The corrosion figures were obtained by in- 

 creasing the temperature of the saturated solution, from which 

 the crystals had grown, about two degrees. When the warm 

 (comparatively) mother liquor had reacted for sixty seconds 

 the crystals were removed and quickly dried with filter paper. 

 The figures resulting in fig. 12 are those formed on the front 

 face of the left hemi prism 110. Those on the parallel face 

 110 are seen in fig. 13. As the corrosion figures on the paral- 

 lel faces are similar, we conclude that chalcanthite is centro- 

 symmetric triclinic. 



Rhodonite. — Fragments of rose-colored crystals from Lang- 

 bangshytta, Wermland, Sweden, were treated for one minute 

 with a warm mixture of equal volumes of concentrated sul- 

 phuric and hydrofluoric acids. As this mineral is very rich in 

 crystal forms and exhibits many different types, accordingly 

 having only fragmentary crystals to work upon, it was difficult 

 to determine with certainty the symbols for the faces. The 

 corrosion figures from two parallel faces are represented in 

 figs. 14 and 15. The faces in question were largely developed, 

 striated and were cut obliquely by the two principal cleavages, 

 presumably (110) and (110). Though not certain, I have 

 assigned the figures to the basal pinacoids 001 and 001 accord- 

 ing to Dana's crystallographic orientation of the mineral. The 

 striation referred to is parallel to the longer direction of the 

 etching figures. The corrosion pits are such as to warrant the 

 conclusion that the mineral is centro-symmetric triclinic. 



Albite. — The material employed for this examination con- 

 sisted in two or three small water-clear crystals from the Alps. 

 Cleavage fragments parallel to (001) were easily prepared, on 

 which the angle of optical extinction was measured under the 

 microscope and found to be +4° 54/, thus proving the crystals 

 to be a plagioclase free from lime, that is albite. By treating 



