Most volcanoes occur at plate boundaries, where two plates are moving away (diverging) or together (converging). A few volcanoes like the Hawaiian Islands form from a hot spot, or a weak spot in earthâs crust, where magma forces its way to the surface. Volcanic eruptions may be explosive (violent) or effusive (passive), depending on the lava chemistry (amounts of silica and dissolved gases).
Ammolite is a rare and valuable opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of the United States and Canada. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral that makes up nacreous pearls.t is also much less fractured, and therefore the more valuable type of ammolite. As of 2003, Korite International had only mined 30 acres (120,000 mÂ²) of the Kainah deposit. As part of their agreement with the tribe, the company must refill areas once exhausted, and ensure the environment is not adversely affected.
It was designated the official gemstone of the City of Lethbridge in 2007. Ammolite is also known as aapoak (Kainah for small, crawling stone), gem ammonite, calcentine, and korite.The latter is a trade name given to the gemstone by the Alberta-based mining company Korite International, the first and largest commercial producer of ammolite.he quality of gem ammolite is communicated via a letter grade system, from most desirable to least desirable: AA; A+; A; and A-. However, this system is not yet standardized and some vendors may use their own systems. The grade and therefore the value of an ammolite gemstone is determined by the following criteria: