Cross and Hillebrand—Cryolite from Colorado. 279 
analysis. None of the crystals upon which the faces were well 
formed were superior to those from specimen A, and only 
measurements of the prism angles were made. The face —3°3 
was not observed at all. 
twin structure, and this is frequently polysynthetic. The 
twinning lines are straight and lie parallel to the vertical axis. 
Extinction takes place at 21° 30’—22° or 68°—68° 30’ from the 
twinning line, in opposed directions in alternate Jamine. Ac- 
cording to Professor Groth the bisectrix is in the plane of sym- 
metry and inclined: 68°5’ forward from the vertical axis. 
Sections parallel to the base show the twinning structure also, 
the line lying parallel to the orthodiagonal. 
A large part of the purest crystals and pyramids from this 
Specimen were used for chemical analysis and repeated water 
determinations, the results of which are given below ‘ 
page 281). 
Chemical investigation. —Previous to the analysis by J. 
Brandl’ of pachnolite carefully selected by Professor Groth, 
pachnolite and thomsenolite were considered to possess the 
same chemical composition. The results of all earlier analyses, 
excluding such as referred to manifestly very impure material, 
while frequently deviating materially from the figures required 
y theory for the formula NaF, CaF’, AIF,, H,0, still agree on 
the whole very well, as shown in the accompanying table, and 
fully justified the belief in the chemical identity of the two 
pecies : 
THOMSENOLITR. PACHNOLITE. 
§ _ | - ety ener 
= to : eo ’ 
3 & S ‘ | vom Rath! ap CaFs, AIFs, 
- i ty M H,0. 
Al....| 13-43] 13°74 || 13-14 | 12:50! 13-46] 12°93] 10°37| 12°32 
Ca...) 17-84 79 || 17°25 | 18°17| 18°10] 17°99] 17-44] 17°98 
Na ___| 10°75} 10°10 || 12-167| 10°23/ 10°68 12:06] 12.04] 10°34 
H20_.| 820] 9-00) 9-60 8°63 810 
F _...| 49°78 | 50-37 pee 51°54 5115] 61°26 
100-00 |100-00 || 102-94/ 100-63 99.63| 100°00 
, Ann. 4. em., cexili, p. 6. 
, Neues Jahrbuch fiir Min., ete., 1876, p. 851. 
4 LToceedings Acad. Sci. of Philad., 1876, p. 42. 
,; Annalen der Chemie und Pharmacie, i 
Si in Ges, far Natur- und Heilkunde, 1860, xx, p. 141. 
¢ wzungsbericht d. nied bet 
This Journal, 1866, II, xli, p. 119. 7 Also 10°80 and 10°81. 
