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Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangeish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals.
Egyptian faience is a non-clay based ceramic composed of crushed quartz or sand, with small amounts of calcite lime and a mixture of alkalis, displaying surface vitrification due to the soda lime silica glaze often containing copper pigments to create a bright blue-green luster. [7]
Substitution of iron and other tri-valent elements for aluminium result in the color variations. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.4. Crystals show pleochroism from red to blue to violet. Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.
Quartzite is a very hard rock composed predominantly of an interlocking mosaic of quartz crystals. The grainy, sandpaper-like surface is glassy in appearance. Minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization, causing streaks and lenses to form within the quartzite. [ 1 ]
Sioux Quartzite at Falls Park, Sioux Falls, South Dakota Cross-bedding in the Sioux Quartzite, Blue Mounds State Park, Minnesota, United States.. The Sioux Quartzite is a Proterozoic quartzite that is found in the region around the intersection of Minnesota, South Dakota, and Iowa, and correlates with other rock units throughout the upper midwestern and southwestern United States.
Quartz crystal with chlorite inclusions from Minas Gerais, Brazil (size: 4.2 × 3.9 × 3.3 cm) Chlorite is a common mineral, found in metamorphic, igneous, and sedimentary rocks. It is an important rock-forming mineral in low- to medium-grade metamorphic rock formed by metamorphism of mafic or pelitic rock. [9]
Deep blue kyanite Kyanite within quartz, Hunterian Museum, Glasgow. Kyanite is an aluminum silicate mineral, with the chemical formula Al 2 SiO 5. It is typically patchy blue in color, though it can range from pale to deep blue [6] and can also be gray or white or, infrequently, light green. [7]
For many years, the source of amazonite's color was a mystery. [20] Some people assumed the color was due to copper because copper compounds often have blue and green colors. [20] A 1985 study suggests that the blue-green color results from quantities of lead and water in the feldspar. [20]