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The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass ...
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.
Llanite – Type of mineral – A hypabyssal rhyolite with microcline and blue quartz phenocrysts from the Llano Uplift in Texas; Luxullianite – Rare type of granite; Mangerite – Plutonic intrusive igneous rock, that is essentially a hypersthene-bearing monzonite; Minette – A variety of lamprophyre
Rhyolite was mined there starting 11,500 years ago. [32] Tons of rhyolite were traded across the Delmarva Peninsula, [32] because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads. [33] Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times. [34]
The ancient Ballena River brought rhyolite-gravel, or "Poway" clasts, from a region in present-day Sonora, Mexico to the Pacific Ocean. Its sediments deposited into an alluvial fan –submarine canyon–submarine fan complex extending for miles offshore.
The Carbaugh Run Rhyolite Quarry Site is an archaeological site in Franklin Township, Adams County, Pennsylvania, United States. It is composed of two smaller sites: a group of small quarries on top of Snaggy Ridge, and the remnants of what may have been a campsite along Carbaugh Run below the ridge.
Susquehanna broad projectile point from central New York State. Made from rhyolite, probably quarried near Gettysburg, Pennsylvania.. Susquehanna broad projectile points are stone projectile points manufactured by Native Americans in what is now the Northeastern United States, generally in the time interval of 1200–700 BC.
Orbicular jasper from Madagascar. Orbicular jasper is a variety of jasper which contains variably-colored orbs or spherical inclusions or zones. In highly silicified rhyolite or tuff, quartz and feldspar crystallize in radial aggregates of needle-like crystals which provide the basis or seed for the orbicular structure seen in this kind of jasper. [1]
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