239 



681. AROENTITE. (Sulphuret of Silver, Silver Glance.) 



a. In small aggregated crystals. 



Note. This specimen consists of small tufts of crystal scattered over 

 the surface of galena. 



BARIUM. 



682. WITHEBITE. (Carbonate of Baryta.) 



a. Translucent crystalline lamps. 



Note. Used in making plate glass and beetroot sugar. See Dana, 

 Mineralogy, p. 697. 



683. BARITE. (Barytes, Heavy Spar, Gawk, Bolognan Spar.) 



a. A large tolerably perfect crystal. 



6. A mass of translucent tabular crystals. 



c. A mass of opaque tabular crystals. 



d. Massive. (Caivk.) 



e. Stalactitic, polished, containing sulphate of calcium from 



Matlock. 



Note. Specimen a is about four inches long and three inches broad, and 

 two deep. Specimens c and d were presented by Mr. H. Pound. For a fig. 

 of crystals, see Dana, Mineralogy, p. 616. 



STRONTIUM. 



684. STRONTIANITE. (Strontian Spar, Carbonate of Stroutiau.) 



a. Crystallized. Two specimens. 



Note. Both Htrontianite and Withenite frequently contain calcium 

 carbonate. See Dana, Mineralogy, p. 699. 



685. CELESTINE. (Sulphate of Strontian.) 



a. Crystallized. Two small specimens. 



Note. These are very pure specimens from the Keuper marls at Bristol. 

 See Dana, Mineralogy, p. 619. 



CALCIUM. 



686. CALCITE. 



a. Rather large crystals, scarcely translucent. 

 6. Smaller crystals. 



c. Tabular crystals, very white, presented by Mr. H. Pound. 



Note. Specimen c resembles in appearance the crystals of sulphate of 

 barytes. Dana, Mineralogy, p. 670, fig. 653 a. Specimens a and 6 are 

 more like those of rock crystal. Dana, Mineralogy, p. 672, fig. 569, from 

 which they are easily distinguished by effervescing with acids. 



d. Minute crystals, from oolite. 



e. Massive, with a layer of gypsum on its surface. 



Note.- For a fine rhombohedron of Iceland spar, see collection of cryt- 

 talline forms in Case No. 9. 



