Exogangue

The exogangue is composed of diatom fragments with minor amounts of volcanic ash, very fine quartz and feldspar grains, sponge spicules, and organic matter.

Source: wiktionary

The winnowing away of siliciclastic exogangue in nearshore locations is capable of converting a commercially low-grade deposit into a more uniform high-grade one.

Source: wiktionary

The observation O.E.K’s phosphates under binocular magnifying glass, after mixing simples with water shows that: the phosphatic elements are primarily made up of pellets, osseous remains, tooth of squales and oolites; the exogangue is composed of quartz, calcite, dolomite, gypsum and clay; the endogangue is not very abundant about 3%.

Source: wiktionary