feldspar

American  

[feld-spahr, fel-] / ˈfɛldˌspɑr, ˈfɛl- /

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.

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feldspar British  

/ ˈfɛldˌspɑː, fɛldˈspæθɪk, ˈfɛlˌspɑː, fɛlˈspæθ- /

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

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feldspar Scientific  

/ 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.

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Other Word Forms

• feldspathic adjective

Etymology

Origin of feldspar

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

Example Sentences

Scientists studying tiny feldspar crystals inside Australia's oldest volcanic rocks have uncovered new clues about the early history of Earth's interior, the formation of continents, and the origins of the Moon.

From Science Daily • Jan. 10, 2026

"Researchers were considering several ideas why feldspar is such an effective nucleation seed," says Prof.

From Science Daily • Jan. 9, 2024

The researchers also used a technique called optically stimulated luminescence to determine when grains of quartz and feldspar in the adjacent sediments were last exposed to sunlight.

From Scientific American • Sep. 20, 2023

The feldspar grains from sediment encasing the logs showed they were about 476,000 years old.

From Science Magazine • Sep. 20, 2023

Several of the homes on the way to the quarries were built from huge blocks of granite, containing quartz, feldspar, and mica, all visible to the naked eye, as Fred once showed me.

From "The Line Tender" by Kate Allen