118 Proceedings of the Royal Society 
mineralogists both in form and chemical composition, and not with 
heulandite. It is rather unfortunate that heulandite is known as 
stilbite by some mineralogists ; stilbite is also known as desmine 
(Breithaupt) by others. 
The lower part of the small specimen is in the form of an 
incrustation of about to of an inch in thickness, from which 
flat plate-like crystals project at various angles. The lower layer is 
compact, and presents a mammillated surface where exposed to view, 
and its fractured edges present a series of small radiate fan-shaped 
cleavage planes, with a well-marked pearly lustre. 
The larger of the projecting platy crystals are about J inch long 
by from \ to broad, and not more than about ~ inch thick. 
They are built of plates of more or less imperfectly developed 
flattened prismatic crystals. This structure tends to impart a sheaf- 
like appearance so common in stilbite. The crystals are semi- 
transparent and practically colourless. Parallel to the principal 
cleavage planes the lustre is strongly marked and pearly ; vitreous 
on the other faces. They are brittle and cleave readily parallel to 
the brachy diagonal ; less readily parallel to the macrodiagonal. 
The faces developed in the specimen are the brachy- and macro- 
pinacoids capped with the planes of the pyramid. The planes of 
the pyramid and of the macropinacoid are small ; the brachy- 
pinacoids are large • the basal pinacoids, so commonly present, are 
undeveloped. Hardness about 4. 
The specific gravity of the mineral in fragments was found to be 
2 ’24 to 2*25, but when reduced to powder it rose to 2*29, thus 
showing the presence of sensible cavities. 
Before the blow-pipe it exfoliates, intumesces, curves outward into 
vermicular forms, and fuses to a white enamel, and is decomposed 
by boiling hydrochloric acid without gelatinising. The lower in- 
crusting portion of the specimen colours the flame much more 
strongly yellow, does not intumesce to the same degree, and is 
decomposed by hydrochloric acid, with the separation of gelatinous 
silica. It is therefore apparently not the same zeolite as the 
crystals, but is most probably sphaero-stilbite. I much regret that 
I had not sufficient to permit a quantitative analysis being made of 
it also. 
