cryptocrystalline


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cryptocrystalline

[¦krip·tō′krist·əl·ən]
(geology)
Having a crystalline structure but of such a fine grain that individual components are not visible with a magnifying lens.

cryptocrystalline

A rock texture that is too fine to be discernible with an optical microscope.
References in periodicals archive ?
The secondary minerals nontronite and locally celadonite represent the first crystallised species lining the outer part of the cavities Other mineral phases occurring during the early stage were calcite and cryptocrystalline silica Nontronite was probably formed by basalt devitrification due to hydration, although ferromagnesian mineral phases present in the basalts might have also contributed to its formation.
The breccias are multi-clastic and have a cryptocrystalline to opaline silica matrix.
Petrographic observation of the samples analyzed in the present study, as well as the samples studied by Plymate and others (1992) and Plymate and others (2001), reveals that the feldspars are significantly clouded by alteration to cryptocrystalline clays, mica, and/or hematite.
Both magnetic metallic crystalline and nonmagnetic cryptocrystalline glass MS were separated from sediments excavated from what appears to be the bottom of a late Pleistocene or early Holocene ice dam lake situated along the banks of the Colorado River about two and one-half miles west of the Colorado-Utah state line.
Gold mineralization occurs primarily in altered, pyrite-bearing argillites and occasionally siltstones, and in the underlying massive sandstones with zones of grey cryptocrystalline quartz veining and strong silicification.
A sample of 2097 lithic items from the Meier and Cathlapotle assemblages (representing 29% and 13% respectively of the sites' fine-grained, non-projectile point, non-core, cryptocrystalline silicate artefact assemblages; see Figure 6 for representative artefacts) was drawn from analytical units sampling the ends and centres of each plank house.
Also, much of the silicate mineralogy is so fine-grained that identification by optical means is difficult to impossible, hence the need for using an X-ray diffraction (XRD) technique which is particularly suitable for discerning individual mineral components of the cryptocrystalline phases and for proper differentiation of carbonate minerals into calcite and dolomite.
Crystals are small (<3 mm maximum diameter) and include rounded embayed quartz, subhedral K-feldspar (anorthoclase, based on the presence of fine-scale cross-hatch twinning), and subhedral plagioclase set in a locally spherulitic groundmass of cryptocrystalline quartz and feldspar.
As noted earlier, blue/purple cryptocrystalline encrustations also believed to be vivianite have been found on the creek cut bank clays and on gravel of the point bar.
You won't see any crystal structure in this green stone as it's a cryptocrystalline mineral with the slightly ungainly name of chrysoprase, cryptocrystalline referring to the microscopic nature of its crystals.
Classic Neuburg Siliceous Earth is a mixture of lamellar kaolinite and corpuscular, cryptocrystalline and amorphous silica.