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.[1] The texture common in these rocks include clusters of divergent or radiating irregular feldspar laths in a fine grained matrix.
Typically they occur as dikes or as thin sills, often in association with nepheline syenite; and they seem to bear a complementary relationship to certain types of lamprophyre dikes. Though nowhere very common they have a wide distribution with occurrences in Scotland, Wales, Massachusetts, Ontario, Portugal, Bohemia, and other places.[1]
The term was widely used in the geologic literature of the late 19th and early 20th centuries, but is currently being discouraged in petrologic usage.
References
- 1 2
One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Bostonite". Encyclopædia Britannica. 4 (11th ed.). Cambridge University Press. p. 297.
- Dictionary of Mining, Mineral, and Related Terms, U. S. Bureau of Mines, 1996
- Williams, Howel; Turner, Francis J.; and Gilbert, Charles M.; 1954; Petrography; W. H. Freeman.