R6 Rhyolite (banded)

3D Model

A scan of Rhyolite from the CQUniversity Mineral Kit. Overall the rock is very light denoting a high silica content (these are termed felsic rocks i.e. full of feldspar and silica – fel = feldspar and sic = silica). The classification of rhyolite is based on its silica chemistry i.e. >65% Silica. This can be estimated (%) by its overall (whole sample) highly felsic nature (whitish/light colours) using percentage proportion tables. Also present are phenocrysts (larger crystals) of mainly quartz and orthoclase felspar in a finer matrix composed of the same minerals. The matrix is termed aphanitic (very find grained and in some cases glassy looking i.e. individual minerals cannot be discerned and identified with naked eye or hand lens). The magma from which this rock is derived usually has a fairly low temperature (850 degrees C) and a high viscosity. Students need to identify and differentiate that this specimen is not a sedimentary rock, which is another rock group that has layering.