Crystallization in the Mineral Kingdom. 137 



spar, should be examined for this purpose. Is it not possible 

 that different species of this mineral may be discovered, when we 

 reflect that specimens from more than a hundred localities may 

 be found in collections ? I have found the sp. gr. to vary from 

 3-017 to 3*324. Is it not possible that a fluor-spar might be 

 discovered having one optical axis ? Who can boast of having 

 undertaken optical or crystallographical researches on this mine- 

 ral ? If we estimate the number of the systems of crystallization 

 by the important mathematical differences which we have here 

 described, and which are in part only slightly marked, in the 

 same way that the old rhombic system has been divided into four 

 systems, we must form thirteen systems of crystallization, which 

 are divided into four groups after the old ones : — 



1st Group. Tesseral System. 



A. Isometrical tesseral, without optical axis. Spinelle. 



B. Anisometrical tesseral, with one optical axis. 



1. Tetragonalized tesseral. Some of the garnets. 



2. Hexagonalized tesseral. Boracite, iron pyrites, cobaltine. 



2nd Group. Tetragonal System. 



A. Symmetrical tetragonal, one optical axis. Zircon, rutile. 



B. Asymmetrical tetragonal, two optical axes. 



1. Monasymmetrical tetragonal. Idocrase. 



2. Diasymmetrical tetragonal. Anatase. 



3rd Group. Hexagonal System. 



A. Symmetrical hexagonal, with one optical axis. Carbonates 



of lime, &c, quartz, beryl. 



B. Asymmetrical hexagonal, two optical axes. 



1. Monasymmetrical hexagonal. Some apatites, clinochlore, 



and other micas, Turmalinus amphibolicus, Turmalinus 

 ferrosus (B. M. pp. 704, 706). 



2. Diasymmetrical hexagonal. Turmalinus hystaticus, Tur* 



malinus dichromaticus, Turmalinus medius, Turmalinus 

 calaminus (B. M. pp. 698, 700, 703, 704). 



4th Group. Heterogonal t } or Rhombic System, 



A. Holoprismatic. 



1. Symmetrical heterogonal. Anhydrite, Arragonite, cymo- 



phane. 



2. Monasymmetrical heterogonal. Sulphate of iron, blue 



carbonate of copper, epidote, pyroxene, amphibole. 



B. Hemiprismatic. 



1. Diasymmetrical heterogonal. Adularia, pegmatolite. 



2. Triasymmetrical heterogonal. Pericline, microcline, tetar- 



tine, axinite. 

 Phil Mag, S. 4. Vol. 20. No. 131. Aug. 1860. L 



