MINERALOGY OF BLACK LAKE AREA. 
71 
The analysis of the original loganite 1 is reproduced in column 2 
above, and it is interesting to note the close correspondence in composition 
between this and the Union pit material; the SiOs, Al 8 Oj>,and MgO content 
is almost identical in the two substances, but loganite contains appreci- 
ably less water and further has nearly 2 per cent Fe 2 Os, whereas the other 
is essentially free from iron. The resemblance between the two sub- 
stances ceases here, however; they are widely different in their physical 
characters, loganite being described as follows: “Hydrated aluminous 
magnesian minerals, sparry in crystallization are met with in several 
localities among the Laurentian limestone in Canada. The first one to be 
mentioned occurs at the Calumet falls. It is associated with pale green 
serpentine, brown phlogopite, and apatite, in a white crystalline lime- 
stone, and has been described by the name of loganite. It occurs in 
short thick oblique rhombic prisms, replaced on the edges or on the acute 
solid angles. The crystals are generally rounded, but present a prism 
of 124 degrees, or near to that of hornblende. There is a distinct cleav- 
age with the sides and the base of the prism, and an imperfect one with 
the longer diagonal. The hardness of the mineral is about that of 
calcareous spar, and its specific gravity is from 2 * 60 to 2 * 64. The surface 
of the crystals is dull, but the lustre of the cleavages is vitreous and 
shining. The colour is clove-brown or chocolate-brown, and the mineral 
is sub-translucent, brittle, and with an uneven fracture. The crystals, 
which are seldom more than one-fourth of an inch in diameter, are 
penetrated by carbonate of lime, from which they are with difficulty freed. 
The mineral is infusible before the blowpipe, and partially decomposed by 
acids. . . . The composition [in the analysis reproduced above] is calculated 
for 100 parts, excluding the carbonate of lime.” 
Loganite is generally regarded as a member of the chlorite group 
of minerals, and, more particularly, as a variety of penninite. It is 
nearly related to, or identical with, pseudophite, which has a very similar 
composition, but contains 2 or 3 per cent less water (see analysis in column 
3 above). Pseudophite, which occurs associated with enstatite at the 
Berg Zdjar in Aloisthal, Moravia, and elsewhere, is described 2 as being 
a compact massive substance, without cleavage, which resembles serpen- 
tine (whence the name from naevdos false, and ophite or serpentine); 
H = 2 * 5 ; sp. gr. = 2 • 75-2 -77; lustre, weak ; colour, greyish-green, olive- 
green, pistachio-green; feel, unctuous. 
The present material thus somewhat resembles pseudophite in its 
general physical characters, except as regards colour and specific gravity, 
but it contains considerably more water. 
1 Geol. of Can., 1863, p. 490. 
* Dana, Mineralogy, 6th edition, p. 652. 
