Dating igneous volcanic rocks
Minnesota, however, has lots of rockhounding opportunities beyond Lake Superior Agates.
Although many people are aware that Minnesota was impacted by the most recent Ice Age, non-rockhounders often are unaware of Minnesota’s volcanic past or that vast seas once covered it.
A volcanic rock is a fine-grained type of igneous rock whose matrix usually consists of glass and tiny crystals.
Through the rapid cooling of molten lava such that no crystallization of its quartz and feldspar contents occurs, the natural glass variety called obsidian is formed.
Those igneous rocks that solidified at or very near to the surface are volcanic rocks.
Igneous rocks are one of the three main groups in standard rock classification; the other two are sedimentary rocks and metamorphic rocks.
Promoted as “andesine” and purportedly from mines in Congo or Tibet, this material was subsequently found to be treated, but the resulting furor hindered the public’s trust in natural copper-bearing feldspar.
Despite this setback, Oregon sunstone miners have strived to rebuild the market, and there are signs of renewed consumer interest in their one-of-kind gem.
This geologic history, however, is important and, as a result, Minnesota has a variety of igneous, sedimentary, and metamorphic rocks.
Rockhounding Tip: Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders.