feldspar

[ feld-spahr, fel- ]

noun

1. any of a group of minerals, principally aluminosilicates of potassium, sodium, and calcium, characterized by two cleavages at nearly right angles: one of the most important constituents of igneous rocks.

feldspar

/ fɛldˈspæθɪk; ˈfɛldˌspɑː; fɛlˈspæθ-; ˈfɛlˌspɑː /

noun

1. any of a group of hard rock-forming minerals consisting of aluminium silicates of potassium, sodium, calcium, or barium: the principal constituents of igneous rocks. The group includes orthoclase, microcline, and the plagioclase minerals

feldspar

/ fĕld′spär′,fĕl′- /

1. Any of a group of abundant monoclinic or triclinic minerals having the general formula MAl(Al,Si) 3 O 8 , where M is either potassium (K), sodium (Na), or calcium (Ca) or less commonly barium (Ba), rubidium (Rb), strontium (Sr), or iron (Fe). Feldspars range from white, pink, or brown to grayish blue in color. They occur in igneous, sedimentary, and metamorphic rocks and make up more than 60 percent of the Earth's crust. When they decompose, feldspars form clay or the mineral kaolinite.

Derived Forms

• feldspathic, adjective

Word History and Origins

Origin of feldspar¹

1750–60; feld- (< German: field) + spar ³; replacing feldspath < German ( Feld field + Spath spar)

Word History and Origins

Origin of feldspar¹

C18: from German feldspat ( h ), from feld field + spat ( h ) spar ³

Example Sentences

Sienite and feldspar succeeded in our descent to the snow line, where we found a felspathic granite.

From Project Gutenberg

The feldspar exhibited its splendent black crystals in fine relief in the massy quartz.

From Project Gutenberg

What little feldspar there was is reduced to quartz and mica, and the quartz pebbles are drawn out into lenses.

From Project Gutenberg

This was materially assisted by the weak lath shapes of the feldspar and the mobility of the micas.

From Project Gutenberg

The appearance of the rock is not modified by the amount of feldspar which it contains.

From Project Gutenberg