Bostonite

Bostonite, in petrology, is a fine-grained, pale-colored, grey or pinkish intrusive rock, which consists essentially of alkali-feldspar (orthoclase, perthite, anorthoclase, and albite). Some samples may contain a small amount of interstitial quartz and others may have a small percentage of calcium present in a sodic plagioclase feldspar. Accessory minerals include apatite, zircon and magnetite, with rare biotite, hornblende or pyroxene. They have compositions very similar to the trachytes and are usually grouped with them. The texture common in these rocks include clusters of divergent or radiating irregular feldspar laths in a fine grained matrix.