26 
MUSEUM BULLETIN NO. 27. 
individuals having an extremely thin bladed habit, tabular parallel to 
the brachy-pinacoid, a(010); less frequently they are twinned on 
m(110), and sometimes stout six-sided prisms are met with as the 
result of the repetition of this mode of twinning. 
The bladed crystals occur either as isolated individuals or in radiated 
or tufted groups, implanted upon the vesuvianite or other matrix; they 
measure less than 1 mm. across the blades, with a length up to about 
3 cm., and they are seldom doubly terminated. The forms most fre- 
quently present are: a(010), m(110), v(031), i(021), k(011), x(012), 
p(lll) and n(122); of these, the domes (v,i,k,x) and the unit pyramid 
(p) are usually developed to about the same size, but n was only observed 
as a narrow line face truncating the edge between k and p. In the prism 
zone, the brachy-pinacoid a is present almost to the exclusion of the 
prism m in the bladed crystals, but at times the mineral presents a 
different habit, with the prism (m) as dominant form, as shown in 
Figure 3. It may also be noted that in several of the crystals examined 
the forms m and a do not form a true prismatic zone, being in reality 
an extremely steep pyramid and brachy dome, respectively, inclined 
to the vertical axis at angles of from 3 to 8 degrees. 
The twin crystals show two or more individuals in juxtaposition 
without re-entrant angles; a common type is illustrated in Figure 4. 
They exhibit the same forms as the simple crystals, except that n (122) 
was not noted; the dome x(012) also is usually not so large as the other 
forms. 
Aragonite in acicular crystals was also observed filling small cavities 
in crystalline masses of amber grossularite from the Hall chrome pit. 
HYDROUS CARBONATES. 
HYDROMAGNESITE. 
Hydromagnesite is most frequently associated with brucite, of 
which it is the common alteration product. It forms stellate groups of 
radiated acicular crystals, having a white colour and somewhat silky 
lustre. Under the microscope the crystals show parallel extinction, and 
in convergent light an optic axis is usually seen to emerge obliquely, the 
plane of the optic axes lying at right angles to the length of the blades. 
The mineral also occurs as a white chalky incrustation. The best speci- 
mens collected came from the American asbestos pits, but good speci- 
mens were also obtained at the Consolidated Asbestos and Chrome 
property from a new pit operated by Mr. Chretien; at the latter locality 
the radiated groups of needles, associated with the chromite, have an 
azure-blue colour which was found, on microchemical analysis, to be due 
to nickel. 
