feldspathoid, felspathoid Min.
(ˈfɛldspəθɔɪd, ˈfɛlspəθɔɪd)
[f. fel(d)spath (see feldspar, felspar) + -oid.]
Any of a group of minerals chemically similar to the feldspars, but containing less silica. Hence ˌfel(d)spaˈthoidal a.
| 1896 J. F. Kemp Handbk. Rocks i. 6 (heading) Feldspathoids. With the feldspars are placed two other important and closely related minerals, nepheline and leucite. Ibid., The feldspars, together with the feldspathoids nepheline and leucite, are the most important of the rock-making minerals in their relations to the classification of rocks. 1910 Bull. Geol. Soc. Amer. XXI. 87 Monzonite may not be rich in alkalies nor carry any feldspathoid. 1912 [see felsic a.]. 1930 Geol. Mag. LXVII. 416 The hypothesis of the origin of felspathoidal rocks by reaction between magma and limestone. 1959 C. S. Hurlbut Dana's Man. Mineral. (ed. 17) 500 The feldspathoids are chemically similar to the feldspars, in that they are aluminosilicates of chiefly potassium, sodium, and calcium but with minor amounts of other ions. 1968 Mineral. Abstr. XIX. 234 Carbonate-rich feldspathoidal rocks from Nsala vent. |