156 Mr. Davy's Account of some analytical Experiments 
II. Sensible Characters of the Fossil. 
The most common appearance of the fossil is in small 
hemispherical groups of crystals, composed of a number of 
filaments radiating from a common centre, and inserted on 
the surface of the shist ; but in some instances it exists as a 
collection of irregularly disposed prisms forming small veins 
in the stone : as yet, I believe, no insulated or distinct crystal 
has been found. Its colour is white, in a few cases with a 
tinge of gray or of green, and in some pieces (apparently 
beginning to decompose) of yellow. Its lustre is silky; some 
of the specimens possess semi-transparency, but in general it 
is nearly opaque. Its texture is loose, but its small fragments 
possess great hardness, so as to scratch agate. 
It produces no effect on the smell when breathed upon, has 
no taste, does not become electrical or phosphorescent by heat 
or friction, and does not adhere to the tongue till after it has 
been strongly ignited. It does not decrepitate before the flame 
of the blow-pipe ; but it loses its hardness, and becomes quite 
opaque. In consequence of the minuteness of the portions in 
which it is found, few of them exceeding the size of a pea, it 
is very difficult to ascertain its specific gravity with any pre- 
cision ; but from several trials I am disposed to believe, that 
it does not exceed 2,70, that of water being considered as 
1,00. 
III. Chemical Characters of the Fossil. 
The perfectly white and semi-transparent specimens of the 
fossil are soluble both in the mineral acids and in fixed alka- 
line lixivia by heat, without sensibly effervescing and without 
