MM. Godon’s mineralogical observations. 145 
of small scales of green tale are perceived [Dorchester]. Perhaps 
the colour, often greenish, of this mineral, arises from the substance 
of talc disseminated in its mass; this colour appearing, in fact, the 
same with that, which would result from the mixture of a green pow- 
dered talc with a white body, such as chalk or white clay. 
The property of argilloid, of being adapted to sharpen instru- 
ments of steel, that is, to produce the effect of a file, whilst it is soft 
enough to be cut with a knife, indicates, that it is formed of an ag- 
gregation of substances, different in their nature, notwithstanding its 
apparent simplicity ; and we are induced to admit that one of those 
cha is silica in the state of quartz. 
- The observations of several chemists icon ascertained the 
presence of fixed alkalies in several rocks of Europe, and Klaproth, 
in particular, having found soda in the klingstein (analogous to our 
sonorous petrosilex), I was desirous to verify these observations in a 
mineral of America. The specimen I selected was of the hardest 
kind of argilloid, very much like sonorous petrosilex. _ Its specific 
gravity was 2.746. Its surface was covered with a light white 
crust. It was taken at Roxbury, about seven miles from Boston, 
not far from the line, which separates this town from Dorchester. 
Chemical examination of argilloid. 
$2. One hundred parts of this mineral (600 grains), reduced to 
a subtile powder, were mixed with equal parts of concentrated sul- 
phuric acid. The mineral having been previously warmed, the mix- 
ture acquired a degree of cohesion nearly equal to the former hardness 
of the stone. Exposed for some time (about 15 days) to the open 
air, cautiously defended from the access of foreign bodies, the mixture 
. a9 
