Composition of several Mineral Substances. 371 
The result of the analysis shows that the quantity of oxygen 
in the silicic acid is twice as great as that contained in the 
bases, from which the formula R, 8, results, which perfectly 
agrees with the composition of augite hitherto examined. The 
proportion of the bases is however different from any former 
analysis. 
In most of the augites from volcanic districts the quantity 
of alumina amounts to about 6 per cent., and with it is pre- 
sent a considerable quantity of magnesia, while the protoxide 
of iron amounts at most to 12 per cent. In these crystals of 
augite the protoxide of iron and the lime are present in nearly 
equal atoms, the magnesia and alumina only in small quanti- 
ties, so that these belong to the class of lime-iron augites*. 
Analysis of a new Mineral— Hydrotalcite. 
This mineral was examined at the request of Dr. Marchand, 
who received it from Professor Scheerer; it accompanies the 
steatite from Snarum, and has the appearance of foliated talc: 
the first result of the examination showed the entire absence 
of silex, while talc contains a considerable quantity. It is 
massive, investing steatite in foliated masses, white, giving a 
white streak with a mother-of-pearl lustre, transparent, flexi- 
ble, with a soapy feel; hardness = 2. Heated in a tube it 
- gives off much water ; at a red heat it becomes reddish yellow; 
dissolves nearly completely on boiling with acids. 
Composition. Containing Oxygen. 
Mapnesia........ 86°30 «2... 14°15 
Feiss. c eae arene ted by 7-97 
Peroxide of iron... 6'90f ****’ 
Carbonic acid ..... 10°54 .«s0+ 7°62 
Ve pate cye ches nO OO) + ernst oe BO 
Insoluble residue... 1°20 
99°60 
* The analysis by Rose of Hedenbergite from Tunaberg nearly agrees 
with the above. 
PIMLICICIACID s ccceeccercasdcaseaistias bareccakt 49:01 
Provowide of 1700 !. 2.00335 st5ief,5.080000288 26:08 
TAM 505452855 0060 ba 5s coddUATAE ASIAN tse 0 nes 20°87 
Magnesia (containing manganese)...... 2:98 
98:94 D.Rep. 
The analysis of the reddish-brown malacolite of Dagero in Finland by 
Berzelius, is still more similar in composition. 
PINGIC BUI vesectagatarvdsteeuseriscesee stakes 50° 
Protoxide: of 17On ics. sezececsscrsdiascesats 18°85 
Protoxide of manganese....,.....ss..0000+ 3 
MaQn@elts. 2.15. jspensueogtiveestecessdestiens 4°50 
VAM Gbeaivecss caodinta asides uses ss cudcdenislass 20° 
Loss upon heating...........06 Vac caqesnaty 0:90 
97:25. ELF. T. 
