28 BULLETIN 118, "UNITED STATES NATIONAL MUSEUM. 



CHALCEDONY, variety PLASMA. 



INDIA. 



Three elliptical buttons; dark blue-green, mottled; average size, 42 by 33 

 by 7 mm No. 1473 



Two pieces, cabochon, elliptical girdle; blue-green; 33 by 26 by 4 and 30 by 



24 by 4 mm No. 1474 



Button, elliptical; gray-green, mottled ; 26 by 19 by 6 mm No. 1472 



Disk, cabochon, elliptical girdle; dark green with white streaks; 53 by 40 

 by 5 mm No. 1475 



CHALCEDONY, variety PRASE. 

 GERMANY. 



Cabochon, elliptical girdle; gray-green; 24.26 carats; 18 by 13 by 11 mm. . . No. 1431 



Saxony. 

 Cabochon-brilliant, elliptical girdle; dull green; 9.735 and 9.45 carats; 20 by 

 13 by 5 and 22 by 12 by 5 mm No. 1430 



CHALCEDONY, variety SARDONYX. 



LOCALITY NOT RECORDED. 



Three pieces, elliptical girdles; red-brown, white, and brown, banded; 43 by 

 29 by 11, 26 by 19 by 8, and 20 by 15 by 7 mm. Colored in Germany. 

 Gift of George F. Kunz No. 540 



Four intaglios, three red-brown on dark brown, one gray on red-brown; 23 

 by 16 to 18.5 by 4 mm No. 542 



CHALCEDONY, variety SIL1C1FIED WOOD. 



UNITED STATES. 



Arizona. 

 Adamana, Apache County: 



Thirty-six stones, cabochon, elliptical and circular girdles; mottled 

 brown, red, yellow, etc. ; 52 by 42 by 9 to 16 by 10 by 5 mm. (figs. 4, 5, 

 pi. 7) No. 824 



Chlorastrolite. — See under Prehnite. 



CHROM1TE. 



Composition. — Ferrous chromite, FeCr 2 4 . 



Crystallization. — Isometric; habit octahedral; usually massive. 



Color. — Black; streak pale brown. 



Luster. — Sub-metallic. 



Hardness. — 5.5 ; rather soft for use as a precious stone. 



Specific gravity. — 4.5 ±0.2. 



Optical properties. — Refractive index extremely high; practically 

 opaque. 



Methods of identification. — Distinguished from jet by its heaviness; 

 from hematite by its streak. 



The mineral occurs in serpentinous rocks, and often accumulates 

 as a " chrome sand" in the beds of streams flowing over such rocks. 



It is used rarely for beads and similar objects, being cut mostly 

 only as a matter of scientific interest; value not exceeding the cost 

 of cutting. 



