Ixxviii Historical Sketch of the Physical Sciences, 1818. 
Idocrase, Gehlenite. 
Silica = HY ear atucs <. 6 > 29°64 
AMUN 50 5-00 5 <ohe le ae a Wades hase 24°80 
a aa Rai oy 9 Stag aes A 35°30 
Oxide of iron... 2... 7°54 hw cenree Uae 
Oxide of manganese... 0°25 .........6. — 
Water cs Cs are car ede ean! Neo gah efatie e 3°30 
The first of these analyses was by Klaproth, the second by 
Fuchs. They do not differ more from each other than two 
different analyses of the idocrase by Klaproth do. 
5. Helvin.—This mineral, as we are informed by Mr. Heuland, 
is found in Brother Lorenz’s mine, near Schwartzenberg, in the 
Saxon Erzgebirge. It was named, it seems, from ‘ys, the sun, 
on account ofits pale yellowish-brown colour. Its primitive form 
is the regular tetrahedron. It is softer than glass, and melts 
before the blow-pipe into a blackish-brown glass. It has not yet 
been subjected to analysis. Hence it has not been determined 
whether or not it constitutes a peculiar species. 
6. Peltum.—This mineral, so named by Werner from its blue 
colour (werd, livor), occurs at Bodenmais, in Bavaria. It is 
crystallized in six-sided prisms, truncated on the edges and 
angles. Cordier says, that in other respects it perfectly resem- 
bles the dichroite. 
7.. Skorodite.—This mineral has been so named by Mr. Brei- 
thaupt, of Freyberg (from cxopodov, garlic); because, when 
“a ee to the heat of the blow-pipe, it gives outa garlic smell. 
It has been found at Slamm Asser, near Schneeberg, in Saxony. 
Mr. Heuland, from its external appearance, considers it as a 
cupreous arseniate of iron. : 
. Tungstate of Lead.—This new species of lead ore has been 
found at Zinnwalde, in Bohemia. It greatly resembles the 
brown acicular phosphate of lead from Poullouen, in Britany ; 
but it crystallizes in very acute four-sided pyramids. 
9. Knebelite.—Dobereiner has thought proper to distinguish 
by-this name a mineral of which a description will be found in 
the Annals.of' Philosophy, xit.392. From his analysis, it appears 
to. be a combination, or mixture, of an atom of silicate of iron 
with an atom of silicate of manganese. It ought, if this be the 
case, to. be-called silicate of éron-and-manganese. The characters 
given of this mimeral are hardly sufficiently precise to characterize 
ity: [I have-dittle doubt: that it has been hitherto confounded 
under the name of grey ore of manganese. Whoever will under- 
take to investigate the-chaos.of minerals at present confounded 
under that name, will undoubtedly discover several new species 
of minerals, and throw light upon the varieties of an ore at pre- 
sent of very cdnsiderable~ importance to some of the most 
interesting branches of our-manufactures. 
10. Texnantite, This is a name given by Messrs..William and 
