troctolite

from The Century Dictionary.

• noun In petrography, a name given by von Lasaulx (1875) to a variety of gabbro composed of lime-soda feldspar and olivin, with a little diallage. Bonney has applied the name especially to the more or less serpentinized forms. Compare forellenstein.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geology A rare type of ultramafic intrusive rock, consisting primarily of olivine and calcic plagioclase