J.D, Dana on Crystalline form and Chemical constitution. 89 
Art. XIL.— Regen Cm and oe lographic Contributions; by 
James D. Dana. No.IV,* Ona connection between Crystalline 
form ae Chemical constitution, with some inferences therefrom. 
G oxyds, the protoxyds, like the metallic elements, are 
charceitialy isometrict in crystallization. The sesquioxyds 
aracteristically hewagonal, this being the form of the 
Se acsycs of iron, aluminum, and chromium. The deutoxyds 
are typically tetragonal, as seen in the deutoxyd of tin (tin ore) 
and of titanium (rutile and anatase). There are other forms 
oer the atom of oxygen as double in its fundamental 
* The preceding papers in this series by the writer are not numbered. They 
are: I, On the Formation of Compound or Twin ced vol, xxx, 275, 296, 1836; 
atk Propose to mig el in the forthcoming edition of et Mineralogy the terms 
Isometric ving a square base), and Orthorh ombic (erect on a a 
oe in ‘lac reopestively of Monometric, Dimetric, and Trimetric. Monomet: 
an a cube; the he al prism is much dimetric as the 
; e died prisms are as truly trimetrte as the right ae: 
It is desirable that the technical terms of science nce should be un 
the World, as far as ible, = that authors should be willing to yield their 0 own 
usage for the sake of anf erms adopted te 
have been have seauity nsive use in Euro ‘sometric is ade 
pe. 
mann's term; tetragonal and hexagonal, with rhombic, are employed by Naumann. 
Mohs's terms pyrami . ramidal for the ne total system, and prismatic for the ortho- 
thombie, are exceedingly bad, as there are pyrami 0 
a. —— as well as the tetragonal; and prisms in all the systems ex- 
e isometri 
There is additional reason, for our proposed change, in in the natural —— of the 
systems of crystallization. For the similarity in the names 
trimetric (the latter two the monodimetrischen and tri eesiins of Hausmann) im- 
a fundamental relation in the forms; while the true classification is as follows: 
1) Isometric, including the isometric system, peculiar in the abserce of double re- 
ion 
™m 
fracti larization ; (2) Isodiametric from equal, and diameter), 
sorters na and hexa; ‘ nal forms sista from the shape of the base), char- 
; by equal transverse axes or ers, and uniaxial polarization; and (3) 
ric (from dwtoos, unequal, etc.), including the remaining systems, and 
tint in having the or diameters all unequal, and biaxial polarization. 
inie, Diclinic, Triclinie (from Naumann) I would retain, as 
. the : 
angular, which would be very objectionable. 2 
Am. Jour. Sci.—Srconp Series, VoL. XLIV, No. 130.—JuLr, 1867. 
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