alumosilikaatide hulka kuuluv kristalliseerunud mineraal
any of a group of crystalline minerals that consist of aluminum silicates with either potassium, sodium, calcium, or barium and that are an essential constituent of nearly all crystalline rocks
Päevakivid on maakoore levinuim mineraalirühm, moodustades keskmiselt 65% kivimite koostisest. Neid leidub peaaegu kõigis tard- ja moondekivimeis, eriti aga graniidis, dioriidis, gneisis ja pegmatiidis.
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Eestis on suuri päevakivikristalle kõige lihtsam leida pegmatiitsetest rändkividest ja rabakividest. Enamasti on tegu kaaliumpäevakiviga, mille pruunid, punakaspruunid või roosakad kristallid on kivimis kergesti tuntavad läikivate lõhenevuspindade järgi.
The feldspars are subdivided into two groups: the alkali feldspars (including microcline, orthoclase, and sanidine), in which potassium is dominant with a smaller proportion of sodium and negligible calcium; and the plagioclase feldspars, which vary in composition in a series that ranges from pure sodium feldspar (albite) through to pure calcium feldspar (anorthite) with negligible potassium. Feldspars form colourless, white, or pink crystals with a hardness of 6 on the Mohs' scale.
Calcium hydrated aluminiosilicate of volcanic origin containing a minimum of 85 % of clinoptilolite and a maximum of 15 % of feldspar, micas and clays free of fibres and quartz.
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