608 ROGERS— THE NOMENCLATURE OF MINERALS. [May 14, 



and neotantalite for the dimorphous forms of zoisite, laurionite, wol- 

 lastonite, boracite, and tantahte respectively. 



Since the rise of colloidal chemistry the question of names for 

 colloidal or amorphous minerals arises. Recently names have been 

 proposed for a few of the naturally occurring amorphous numerals. 

 These substances can hardly be excluded from the list of mineral 

 species as they are definite in composition, unless v^e insist that a 

 mineral must be crystalline in character. To obviate this difficulty 

 Niedzwiedzki® has proposed the term mineraloid for the natural 

 amorphous substances. Among examples of colloidal minerals or 

 mineraloids are the following: ostwaldite = colloidal AgCl (butter- 

 milcherz) ; jordisite = colloidal MoS, ; a-kliachite = colloidal 

 AloOo-HoO; /?-kliachite = colloidal ALOg-aH.O; ehrenwerthite = 

 colloidal FcoOs-HoO. The term sulfurite has been proposed for 

 amorphous sulfur and metastibnite for amorphous antimony sul- 

 fid. Fortunately there are very few amorphous minerals which are 

 definite enough to be recognized as distinct mineral species® but the 

 application of colloidal chemistry to mineralogy will probably in- 

 crease the number in the future. 



Names are used not only for definite chemical compounds, which 

 are often end members of isomorphous series, but also for isomor- 

 phous mixtures such as olivine, rhodolite, epidote, and pisanite ; for 

 double salts such as dolomite and monticellite; for pseudomorphs 

 such as martite, arkansite, and hampshirite ; for mechanical mixtures 

 such as californite and azurlite ; for semiprecious or ornamental 

 stones such as bonamite and satelite ; for artificial substances such as 

 alite, cementite, silver-analcite, soda-leucite, and carnegieite ; for 

 group names such as orthoaugite, clinoaugite, glaucamphibole ; and 

 for numerous varieties based upon crystal habit (e. g., adularia), 

 structure {e. g., pholerite, nemalite), color (e. g., melanite, hiddenite, 

 kunzite), unusual optical properties {e. g., isomicrocline, neocole- 

 manite), and variations in chemical composition due either to 

 impurities, {e. g., johnstonite) or to isomorphous replacement (e. g., 

 cuprogoslarite, paravivianite, titanaugite). Varietal names are 



s Centralblatt fiir Min. Geol. u. Pal., 1909, p. 661. 



^ Of the more common minerals only opal, bauxite, psilomelane, and 

 allophane are amorphous. 



