3i8 The American Geologist. November, i899 
Cketfiical Constitution of Roscoelitc. 15\- Y . W. Ci.arke. (Am. 
J. Sci. 157, 454-455-) 
From the analysis of Hillebrand the author has calculated the em- 
pirical formula to be H453 K-o Fe^a Mgn AUso Vsia Siioa O2724. Consid- 
ering the groups SiOi and SiaOs to be replaceable, the formula reduces 
to R'6,,E."«3 Al-o V318 (SiOOeso (SiaOs) 71. which would indicate, ac- 
cording to Clarke's mica theory, a mixture of three molecules repre- 
senting respectively a normal phlogopite, a trisilicate alkaline biotite 
and a vanadium muscovite, the last forming 74.5 per cent, of the whole 
mass. ^J- L- ^• 
The Occurrence of Roscoetite. By H. W. Turner. (Am. J. Sci. 
157,455-458.) 
In each of the four localities in which this mineral occurs in Cali- 
fornia it is found that the quartz veins, and the associated gold and 
roscoelite occur near the contact of an intrusive granodioryte, either 
with some members of the Calaveras formation (Carboniferous) or 
with a serpentinic rock of late Jurassic or early Cretaceous time. 
The veins are later than the granodioryte and pass into it from the 
surrounding rock without interruption. The intimate association with 
the granodioryte suggests that the mineral may be regarded as due in 
some way to mineralizing solutions following the intrusion of this 
rock. M- L. F. 
On the Chemical Composition of Parisite and a Nezu Occurrence of 
it in Ravalli County, Montana. By S. L. PenField and C. H. War- 
ren. (Am. J. Sci., 158, 21-24.) 
The parisite occurs in a fine grained, friable, white substance re- 
sembling decomposed rhyolyte or trachyte, and is associated with nu- 
merous pyritohedrons of pyrite. It crystallizes in rather long hexagonal 
shafts made up of pyramids in oscillatory combination, and terminated 
by distinct, somewhat enlarged pyramids. A study of the analysis 
made by the authors indicates that parisite is probably a double car- 
bonate of the formula 2(RF)C03 CaCOa or (RF)2 Ca(Co3)3 in which 
R=Ce, La, Di, etc. m. l. f. 
The Constitution of Tourmaline. By F. W. Clarke. lAm. J. Sci., 
158, 111-121.) 
Upon reducing to a comi,Tion basis of six silicon atoms, the formula, 
H..1 AI3 Bg Si4 O21 of Penfield and Foote becomes H,6i Al^i BgSigi^^ 
Ogii, while that of Clarke is Hu AU B3 Sio Ogii- The author holds 
the view that these slight differences amount to no more than the un- 
.certainties of the analyses, and in support of this view gives a series 
of formula! computed from Rigg's data which show variations beyond 
both extremes, and make it probable that neither formula can be 
accepted without qualification as final. The intimate relation of tourma- 
line to mica is indicated by the alteration of the former to mica, by 
the parallelism in composition between the two when they occur togeth- 
er, and by the similafity in the commingling of isomorphous mole- 
cules in the two groups. Allied to muscovite, Al;,(Si04)3KH2, is the 
