ferent colours—blue, when looked at in the direction of its axis, and dark yellow when regarded at a right angle.
It
is found chiefly in hexagonal and dodecahedral prisms. Its cleavage is
concave and unequal. Sometimes, the dichroite, when cut, sends out a
ray of light similar to that of the asteria.
This
substance scratches crystal, and is scratched by topaz ; its specific
gravity is 288 ; it becomes electric by friction, and acquires polarity
by heat. Mixed with borax, it melts into a transparent glass, on which
acids have no power.
Its component parts are magnesia, alumina, and silex, with a little oxide of iron and water.
The
dichroite is found in primitive rocks, in blue chalk, in pyrites of
copper, in the various kinds of quartz, in felspars, and in scattered
flints.
It
is brought from Spain, Bavaria, Greenland, Sweden, Norway, and Finland.
In Ceylon it is found in small blue stones. In Connecticut it is
embedded in granite.
Blue
quartz might be mistaken for dichroite, but quartz is the hardest, and
dichroite offers the phenomenon of double colour, which in the former
does not exist. Many are similar to the sapphire at first sight, but
eventually they are easily to be distinguished by their hardness.
