The
basalt pyroxenum is of a better and brighter green than that found in
lava. It easily marks glass and is translucent ; it has unequal
breakage and very easy cleavage.
Those found on Etna are of a bright greenish black, having a concave though imperfect breakage.
We
cannot declare to a certainty whether crystals of pyroxenum existed
previous to volcanic eruptions, or if they crystallized afterwards, but
the first hypothesis seems the most likely. Some black varieties of
pyroxenum are known by the name of augite ; their dust is brown, and they took this name on account of their brightness, from the Greek αίγη, splendour.
Certain green pyroxenum crystals from the Tyrol, more or less modified irregular octahedrons, received the name of fassaiti, because they are found in the valley of Fassa.
The salilite pyroxenum, formed in crystals, is green and variegated.
The pyroxenum diopsido, much
more rare, and found in transparent crystals of a grey-green and
sometimes white, contains only lime, magnesia, and a small quantity of
protoxide of iron ; the double refraction which its cleavage gives
caused Haüy to give it the name it bears of δυο, two,—οψις, sight,—that is, double view, or mineral which has two distinct characters ; it bears the name of alalite on
account of its being found crystallized in the valley of Ala, near
Turin ; it is dug up in lamina, in the valley of Mussa, in the same
province, and thence called mussite.
