J. D. Dana’s Mineralogical Contributions. 213 
6. Homeomorphism of Romeine, Idocrase, Cerasine, Chiolite, 
Braunite. 
The species have no basal cleavage. 
Romeine, rea Sb) Sb - - O : 1=124° 05/-124° 35” 
Idocrase, R® Si+-# Si : - O : 1(2)=128° 
Cerasine, Fi Cl+Pb - - O : 1=123° 067 
Chiolite, 3Na F-+2Al? FF - - OF T==i287 17” 
Braunite, Mn* - - O : 1=125° 40’ 
ied plane in Idocrase here taken as 1 is usually made the 
plane 
The Scheelite series may be related both to the Apophyllite 
and Idocrase series. In Scheelite (Ga W), O: 1¢=123° 59; in 
Scheeletine. (Pb W), 122° 33’; in Wulfenite (Pb Mo), 122° 26 ; 
in Fergusonite ((¥, Ge)« Ta), 124° 20’. But if the planes 1¢ are 
not homologous with 1 in Apophyllite, and the planes usually 
given as 1 should be retained so, then the angles O:1 are be- 
tween 114° and 116°. In Scheelite, both 1 and 1¢ correspond 
to cleavages, and the formér is most distinct, while the latter is a 
plane of . ‘twin-com position. 
7. Homeomorphism of Sylvanite, Mispickel. 
Srlvanite (Ag, Au)Te? =1108 46) (B.d&:M) 0: 9%==148° 34’ 
pickel, Fe (S, As y: i=i1 O: 4%=148° 56’ 
* Volger i in his Studien zur eo oa = eae oe Zurich, 1854, p. 
421, in an oy sire ae er on mangan nite an altered mineral 
with the € original composit prc si me a poo omceomorphism 
with tin ore a and wattle “i ee angles however are rather remote for such a 
conclusion, much nearer those of *‘docrase, We have evidence in the dimor- 
of idoer net in connectian with the dimorphism o oO e 
men and the pr yds and peroxyds, that a monometric = a rhombo — rd 
= ° to 8 d a dimetric with the form of id y be he three forms of a 
orph, and — it seems possible that a peroxyd (4) may have an idocrase Beg 
Idocrase, as explained beyond, may be viewed as consisting of peroxyds R8, # Si, 
each containing of oxyge me 
dusmannite is suppose a by Volger (p. 414) to be homologous in composition 
With anatase; and Polianite ( (p. 403) ‘which bea ay Géthite in its angles and af- 
Mn on analysis the composition © ite, Mn, is supposed to be an altered 
in H, rendered envi tg by the fisener Manganite, which is generally con- 
sidered #n H, is regarded by him as probably Mn Hi? and “i pt tl ie with an- 
ite (Be 2) 
The “wis undoubted bacty ea of the mange ores are liable to alterations 
by eo ation and om r losing water, so that ook or eet a are yet few in 
makes Brookite homemomorphous with Guth ‘doe cit., p. 483 and 
500). But the resemblance is not close. In Brookite I: ft =99° 5 —100° 30’, and 
that Brookit 
not trimorphous. Sagenite, or acicular rutile in Quartz, he endeavors to 
ct citer Brookite or cram hs of Rutile after Brookite. Brookite is closely 
homceomorphous with Columbite. as shown by the wri writer in this volume, page 86. 
