The Earth’s crust is the most exciting part of our planet – it’s where gemstones are formed and found (with the exception of Diamonds, which form much deeper somewhere in the region between the lower crust and upper mantle). This is all thanks to the powerful eruptions of volcanoes, thrusting all the essential elements needed to form crystals form the depths of our planet. Volcanoes are violent ruptures in the Earth’s crust with hot lava, volcanic ash and gases bursting out of the mantle some 5 – 72km deep. With a whopping 4,000 minerals on earth today, obsidian is one of the more abundant and quickest forming in the world with a range of uses throughout history.
Classified as an extrusive igneous rock, Obsidian is formed from the extremely rapid cooling of felsic lavas, high in silica and aluminum. As a general rule of thumb, the larger the crystals the longer they have had to crystallize. Steady temperatures mean the mineral rich solutions can continue to separate and solidify, through a process called fractional crystallization, and produce large, well-formed crystals. Due to the quick cooling of Obsidian once it reaches the low temperatures of the earth’s surface, the mineral constituents from which it forms do not have time to crystallize.
An amorphous mineral, Obsidian is generally described as a volcanic glass and can be identified by concentric lines/conchoidal fractured surfaces and a vitreous lustre, typical of glass and other silicate minerals. Amorphous refers to a mineral without a clearly defined shape or form and so the material fills cavities and surfaces as a liquid, solidifying in what ever negative space is available rather than crystallizing in defined external forms e.g prismatic Quartz crystal.
With a body color generally appearing as dark brown, greenish, or black due to iron/magnesium impurities, the many named varieties of obsidian refer to the inclusion or colored iridescent sheens it may exhibit. Popular varieties include Snowflake Obsidian with greyish-white spherulites, Mahogany Obsidian, Gold Sheen Obsidian and Silver Sheen Obsidian. On the rare occasion where Obsidian displays a multi-colored sheen, it is knows as ‘Rainbow Obsidian’, a much sought after and popular formation that contains fine, multi-colored, parallel layers. The iridescence is due to fine inclusions of mineral crystals, rock debris or gases trapped under the surface and throughout the stone. In the case of Rainbow Obsidian each layer contains different densities of inclusions and gas bubbles diffracting the light into alternating spectral colors.
Bunny Bedi, owner and designer at Made in Earth, has always been fascinated by the colorful qualities of Rainbow Obsidian. “I’ve been working closely with the talented artisans in Mexico who are experts in carving and polishing obsidian. They creatively cut the material into interesting shapes, hearts and stars are our most popular, to reveal concentric lines of vivid colors within the stone. Purple is my personal favorite, but when we capture a full rainbow it’s a sight to see!”
Worn as a talisman of protection to ward-off negative energies it is also the structural properties of Obsidian that made it a valuable commodity for Stone Age tool makers. Blades or arrowheads could be fashioned by breaking and fracturing the surface into curved shapes with a sharpness finer than that of any steel, down to nearly molecular thinness. Our designer has also captured these in some of our rings and pendants too!
Our Earth is constantly evolving and part of that evolution means the odd outburst from its core in the form of a volcano. These magnificent (and dangerous) products of the earth’s energy mean crystals and minerals are beginning their growth cycle with every fiery explosion. Thankfully for us in the jewelry industry we won’t need to wait millions of years for more Obsidian to form but for our other favorites like Amethyst and Aquamarine what we have now might be all we’ll get to see in our lifetime.