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

Derived Forms

• feldspathic
  adjective

Etymology

Origin of feldspar

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

Example Sentences

That ash contained feldspar crystals, which scientists can date to determine when the eruptions happened, explained ASU geologist Christopher Campisano.

From Science Daily • May 16, 2026

Due to the geometry of the feldspar crystal, these hydroxyl groups are positioned in a way that makes them ideal anchoring points for water molecules.

From Science Daily • Jan. 9, 2024

"It could be due to potassium atoms contained in feldspar, or perhaps certain defects in its crystal structure."

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

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