Felton_1

Felton, John (1595-1628), the assassin of the Duke of Buckingham (q.v.). The elder Dumas has made an important figure of him in The Three rarely with free quartz or hornblende. Most mineralogists now follow Tchermak in considering only three true species of felspar to exist, viz. orthoclase, or potash-felspar, albite, or soda-felspar, and anorthite, or lime-felspar, the other forms being varieties or twin-combinations of these. Orthoclase, a potash-felspar, crystallises in oblique rhombic prisms. When transparent and colourless it is known as adularia, or if with a bluish opalescence as moonstone, both of which forms are gems. More often it is nearly opaque, perhaps from partial hydration, and tinged with a salmon-pink, in which condition it is an abundant constituent of granite, felsite, eurite, and gneiss. It often occurs in large "porphyritic" crystals several inches long. It decomposes into china-clay, or kaolin (q.v.). Sanidine is a glassy, translucent variety containing some soda, and characterising trachytes and liparites. Microcline is a potash-felspar differing slightly in angle, thus becoming plagioclastic: amazon-stone is a valuable green variety. Albite, or soda-felspar, named from being generally white, is plagioclastic, but acid. It occurs in many diorites, syenite, and occasionally in granite. Anorthite, the lime-felspar, is also white and plagioclastic; but is basic, fusible, soluble in acid and heavy. It occurs in some gabbros and other basaltic rocks. Oligoclase, or soda-lime-felspar, is probably a combination of albite and anorthite, in which the former predominates; andesine, or soda and lime-felspar one in equal proportions; and labradorite, the lime-soda felspar, one in which anorthite predominates. Oligoclase commonly occurs with orthoclase in Scotch grey granites; andesine, in the basaltic rocks known as andesites from their occurrence in the Ancles; and labradorite - which is often dark-coloured, and exhibits on some faces beautiful change of colours, blue, green, yellow, red or brown, from included fibres - in basalts, gabbros, and hypersthenites.