What does feldspar mean?
Feldspar is the collective name for a family of rock-forming minerals composed of aluminosilicates of potassium, sodium, calcium, or barium. It is by far the most abundant mineral group in the Earth's crust, making up roughly sixty percent of it, and it forms a principal constituent of igneous rocks such as granite as well as many metamorphic and sedimentary rocks. Geologists divide feldspars into two main groups: alkali feldspars, which are potassium- or sodium-rich, and plagioclase feldspars, which range from sodium-rich albite to calcium-rich anorthite. Beyond geology, feldspar has practical commercial value: ground feldspar is widely used in the manufacture of glass, ceramics, and enamel, where it acts as a flux that lowers melting temperatures. The word carries a neutral, technical connotation, appearing chiefly in scientific writing, though it surfaces in everyday contexts whenever gemstones like moonstone or sunstone — both varieties of feldspar — are discussed.
nounAny of a group of abundant rock-forming minerals consisting of aluminosilicates of potassium, sodium, calcium, or barium, constituting roughly 60% of the Earth's crust.
- Any member of a large group of rock-forming aluminosilicate minerals (including orthoclase, albite, and anorthite) that together make up the majority of the Earth's crust.
- A piece or variety of such a mineral, especially as used commercially in ceramics and glassmaking.
"The pink grains glittering in the granite countertop were flakes of feldspar."
"Granite owes its mottled appearance to interlocking crystals of quartz, mica, and feldspar."
"The pottery industry once relied heavily on mined feldspar as a flux in glazes."
Used when referring to multiple specimens or to different members of the feldspar mineral group; uncountable 'feldspar' remains standard when speaking of the substance generally.
"Plagioclase feldspars form a continuous chemical series from albite to anorthite."
Feldspar makes up more of the Earth's crust than every other mineral combined — and it gets its name from German farmers who found it in their fields.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of feldspar
Feldspar entered English in the mid-eighteenth century, borrowed from the German Feldspat, in which Feld means 'field' and Spat refers to a non-metallic mineral that cleaves readily into lustrous pieces — the same element that appears in the mining term 'spar'. The name arose because early German miners frequently encountered the mineral in tilled fields and surface outcrops. The older anglicized spelling 'feldspath' survives in some older texts, while related terms such as 'feldspathic' and 'feldspathoid' derive directly from it.
Related word forms
How feldspar is actually used
Feldspar is an uncountable mass noun when referring to the mineral as a substance, though it can take plural form when referring to individual specimens or varieties. It belongs primarily to geological, mineralogical, and technical registers rather than everyday speech.
Easily confused with feldspar
Quartz is silicon dioxide and lacks the cleavage planes characteristic of feldspar; the two are often confused because both occur as light-colored grains in granite.