A gem-quality ammonite, "Sandrita" Paraíba tourmaline, Alaskan gold nugget and olivine-freckled meteorite are just a handful of eye-popping treasures that will be offered today at Heritage’s "Nature & Science Signature" auction.
According to the auction house, the "gem" ammonite from the Bearpaw Formation in Alberta, Canada, dates to the Cretaceous period some 71 million years ago. Exhibiting superb iridescence, the specimen is said to be a top representation of the Placenticeras costatum variety, which accounts for less than 10 percent of the ammonites found at Bearpaw.
This extraordinary piece weighs 24 kilograms (52.8 pounds) and offers superb color and an incredible matrix in both size and shape. The vibrant fossil measures 10 inches (25 centimeters) at maximum diameter and is visually stunning with a myriad of vivid reds, oranges, golds and greens, as well as the rarer purples and blues.
Ammolite, the gem, is formed from the fossilized shells of ammonite molluscs, which thrived in an inland sea east of the Rocky Mountains. After sinking to the seabed, the mud that covered ammonites hardened over millions of years to become shale.
The shell properties, combined with southern Alberta’s unique geology, transformed many ammonite shells into the ammolite that is mined and used for jewelry today.
The mineral composition of ammolite is similar to that of a pearl, and the iridescent, multicolor presentation is reminiscent of a fine opal.
Although ammonite fossils are present in many places around the world, ammolite has been found only in one place, the Bearpaw geological formation in southern Alberta, making it one of the rarest gemstones, according to the American Gem Trade Association.
Ammolite is one of the few biogenic gemstones, which means it is made by living organisms. Others include amber and pearl. Ammolite was given gemstone status by the World Jewellery Confederation in 1981.
Another highlighted lot at the auction is a 2.65-carat “Sandrita” Paraíba tourmaline from Brazil. Paraíba tourmalines are named after the Brazilian state in which they were first discovered in 1989. Although this example hails from the Brazil's Batalha Mine — making the color rare for this locality — it still presents with the iconic “Sandrita” green hue associated with the Sandrita Mine in Paraíba.
It has been expertly cut and faceted with modified brilliant faceting, and is clean to the naked eye and when viewed through a loupe. Once a part of the private collection of Heitor Barbosa, who discovered this variety, it later passed through the hands of Paraíba tourmaline expert Brian Cook before ending up in a private international collection.
Bidders also will have a chance to own a gold nugget from Alaska that tips the scales at 5.5 troy ounces and measures just over 2 inches (5.21 centimeters) in length.
Smoothed by natural forces, this nugget has a number of “bubbly” sections resulting in an organic shape. Heritage commented that given the fact that a mere single-troy-ounce gold nugget is as rare as a 5-carat diamond, any such specimen this large is an inherent rarity.
Another remarkable specimen is this slice of Imilac meteorite that was first discovered in Antofagasta, Chile, in 1822. Imilac is a favorite of collectors because of its rarity (they account for fewer than 200 out of more than 70,000 classified meteorites listed in the Meteoritical Bulletin) and because of their beauty. Measuring more than 16.5 inches (42 centimeters) in width, this piece is covered in olivine crystals over its otherwise mirror-like surfaces. Olivine is the non-gem variety of peridot.
Live bidding at HA.com commences today, November 20, at 11 a.m. CST.
Credits: Images courtesy of Heritage Auctions/HA.com.