Greenhorn indeed has much more silica, but not any in the form of tridymite
It should be noted that none of the analyzed samples contained cristobalite or tridymite
, with all of the reported crystalline content resulting from quartz.
The presence of calcite, dolomite, silica (quartz, tridymite
, cristobalite), apatite, clay minerals (smectite and smectite-illite) and rare sulfides in the matrix of natural OS, as well as in the IR of natural oil shale and burning test ash is interpreted from the results of XRD and SEM-EDS analyses.
Although very effective in iron castings, the tridymite
phase change and resulting increase in volume occur at too low of a temperature to prevent veining in steel castings.
Compared with compositions of many other oil shales of the world , including the Estonian Paleozoic kukersite , and graptolite argillite [15-18], the Near East oil shales have specifically high contents of carbonate (calcite), silica (quartz, in places with admixture of tridymite
and cristobalite--unpublished data by the authors) and sulfur .
It is believed this secondary expansion indicates the transformation of the silica from beta quartz to tridymite
Typical high temperature non magnetic minerals found in pyrometamorphic rocks associated with coal combustion appear to include several Fe and Al rich clinopyroxene, melilita, cristobalite, tridymite
, mullite, cordierite and fayalite solid solutions, as well as glass (Foit et al.
Associated minerals are: hematite, cassiterite, quartz, tridymite
, cristobalite, opal, calcite, "zeolites," mimetite and unidentified clay minerals.
The major minerals present in the as received sample are calcite, quartz, tridymite
, apatite and traces of some clay minerals (see Fig.
Hold times are generally applied at 1600-2000F (870-1093C) for 2 hr to accommodate the large volume expansion (12%) during the transformation from beta quartz to tridymite