Note:  Do not rely on this information. It is very old.


Gabbro, a name originally applied to an Italian serpentine containing that variety of augite known as diallage; but now used for a family of plutonic rocks of basic composition and granitoid texture, consisting of anorthite or some allied basic felspar with some ferro-magnesian silicate, such as diallage, augite, or less typically hornblende or olivine. Though essentially noncrystalline, these rocks may be coarse or fine-grained: they have a specific gravity between 2.9 and 3.0; and contain from 48 to 54.6 per cent. of silica, from 10 to 29 per cent. of alumina, from 4.8 to 15.8 of iron-oxides, and from 9 to 18 per cent. of lime and magnesia. They occur in the Lizard district, Anglesey, Mull, Skye, Sutherland, Carlingford, etc., forming intrusive bosses.

“See a flame in a spark, a tree in a seed; see great things in little beginnings; look not so much to the beginning, as to the perfection, and so we shall be in some degree joyful, and thankful unto Christ.”
–Richard Sibbes, The Bruised Reed and Smoking Flax