This specimen is an example of a mineral that formed in a volcanic environment.
When molten, silicate-rich fluids erupt onto the Earth’s surface, minerals often form in the numerous pockets and holes that develop in the cooling lava.
These two cases show minerals that are formed through the activity of volcanic lava flows. One of these cases contains a collection of minerals that has been found in the basaltic lava flows near Paterson in New Jersey approximately 20 miles west of New York City. These minerals did not form in the basalt specifically, but rather in small spaces developed within the basalt. These little pockets, cracks, and fissures contain these minerals, actually secondary minerals, and include such colorful kinds as number 18, prehnite, and number 14, amethyst.
Many of these minerals, too, display exquisite crystal form. Notice number 9, in which the natrolite is featured, or specimen number 17, the specimen of mesolite. To the right of the Paterson collection are minerals that typically have developed in other volcanic areas. Perhaps the most typical mineral that is associated with volcanic activity is specimen number 4, sulfur.