It seems we have been here before! The May gemstone is a repeat of the mineral beryl. Yes, emeralds are a different color than the March gemstone aquamarine, but mineralogically a beryl is a beryl is a beryl.
The striking green color of an emerald is caused by the introduction of just 0.1-0-5 percent chromium substituting into the aluminum spot of the beryllium silicate mineral. A small amount of vanadium is also present. It is truly amazing that just a fraction of a percentage of an element can impart such a striking difference in color. While the richness and intensity in color is paramount in valuing an emerald, the presence of visible inclusions is also important. Emeralds lacking inclusions to the eye are considered flawless and carry more value than those with visible inclusions.
Written for the March 2016 Wayne County Gem and Mineral Club newsletter
The mineral beryl is hard and can sparkle with exceptional clarity and wondrous color when free of inclusions and defects, clearly justifying its lofty gemstone status. In fact, not just one gemstone, but several depending on the color imparted by trace amounts of iron, chromium, manganese and other transition elements substituting into the crystal lattice. Aquamarine, emerald, morganite, and heliodor are all gemstones of the mineral beryl. But it is sky blue variety that has our special attention this month as aquamarine is the March birthstone.
After 3 nights in Cobalt (see August WCGMC newsletter), we headed to Eganville in search of more collecting adventure.
Although the primary objective of our trek back to the Grenville Province was minerals, our first stop was at a limestone quarry where large cephalopods and coral could be found. The Haley Quarry, 8 miles southeast of Eganville, exposes the Lindsey and Verulam Formations of the Upper Ordovician Ottawa Group which are known for their large cephalopods, some of which are exposed in nearby Bonnecherre caves.