The Magnesites produced during these processes usually are in isotropic and cryptocrystalline
forms, often with high grade.
The K3 anhydrite is characterized as milky white, soft to firm, amorphous, microcrystalline to cryptocrystalline
, and is washable.
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.
silica (opal) can precipitate in close proximity to pyrite, and is thought to be derived from weathering of layer aluminosilicate minerals.
As silicified wood and jasper are present in small numbers and are similar cryptocrystalline
rocks, they are combined for this analysis.
Jasper is an opaque, impure cryptocrystalline
quartz, usually red, but also yellow, green, and greyish blue in color.
The typical emerald vein contains 80 [cm.sup.3] of white cryptocrystalline
quartz overlying a 20 [cm.sup.3] open crystal pocket.
Differences in reaction products morphology are also observed: their structures range from isotropic to cryptocrystalline
. The reaction product, initially as the potassium-sodium silicate gel, binds calcium ions and in area situated away from the silica aggregate reactive grain surface it finally becomes a potassium-sodium-calcium silicate.
Galena is present mainly as the common coarse-grained, well-crystallized and friable type, but also displays several other textures, such as fine-grained, sheared, massive, and 'steel' (a dense, extremely fine-grained, almost cryptocrystalline
The terminology used to describe the size of crystals (coarse-crystalline to cryptocrystalline
) in the sedimentary rocks follows that of Poldvere & Kleesment (1998).
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.