VOLCANIC OPALS

MT SHASTA OPAL ROUGH

This is a specimen of rough mined at the base of Mt Shasta in California USA.It is formed of silica but lacks the fire of opal.Some  parts are transparent with a green hue.

Weight 133.05 cts app

Size 67 x 38 x  9 mm app

About 593,000 years ago andesitic lavas erupted in what is now Mount Shasta's western flank near McBride Spring. Over time an ancestral Mount Shasta stratovolcano was built to large but unknown height; sometime between 300,000 to 360,000 years ago the entire north side of the volcano collapsed, creating an enormous landslide or debris avalanche,

The next cone to form is exposed south of Mount Shasta's current summit and is called Misery Hill. It was formed 15,000 to 20,000 years ago from pyroxene andesite flows and has since been intruded by a hornblende dacite dome.