Em busca dos segredos do peridoto

Enquanto os cientistas especulam sobre planetas feitos de diamante evoluindo na galáxia, pelo menos uma pedra preciosa extraterrestre já está entre nós.

O peridoto, uma gema de cor verde azeitona, tem sido encontrada ocasionalmente na Terra, a partir de meteoritos, sendo mesmo trabalhada e facetada em jóias, mas ele é tão raro que dificilmente o encontrará à venda numa joalharia.

No entanto, investigadores do GIA (Gemological Institute of America) reuniram 26 amostras extraterrestres para descobrir a diferença entre elas e as suas congéneres terrestres. Os dados estão publicados na revista de Outono do GIA, Gems & Gemology.

Um extracto:

Peridot is the gem version of a mineral called olivine, an iron and magnesium silicate -- (i.e. containing silicon). Olivine is part of the makeup of our solar system neighbors, including some metallic meteorites that occasionally fall on our home planet. While such peridot-bearing meteorites are rare enough, the intense heat from their journey to Earth and their explosive impact on contact with terra firma ensure that few specimens survive intact. That’s why peridot pieces from outer space are nearly always quite small.

Peridot from Earth’s own deposits was one of the first gemstones treasured by mankind. The ancient Egyptians called it “the gem of the sun” after discovering a deposit in what’s now known as St. John’s Island in the Red Sea. Today, sources include the United States (Arizona, Texas and Hawaii), China, Myanmar and Pakistan, which produces many of the largest, finest specimens. Peridot’s attractive color and relatively modest price have made it popular with jewelry designers around the world.

GIA researchers Dr. Andy Shen, John Koivula and Dr. James Shigley assembled specimens from several terrestrial locales and compared them with 26 samples taken from the Esquel meteorite, the most notable peridot-bearing extraterrestrial object.

Discovered in Argentina about 50 years ago, this massive meteorite contained numerous peridot crystals. An American collector purchased most of the Esquel in 1992 and divided it into a number of sections for sale. Three of the Esquel samples examined by GIA were faceted gemstones, while the others were part of polished slabs.

Using a laser beam and sophisticated mass spectrometry that can detect tiny amounts of elements within gemstones, the GIA team discovered significant differences between earthly and extraterrestrial peridot. Their tests found different levels of lithium, vanadium, nickel, manganese, cobalt and zinc between the two, allowing researchers and ultimately gem buyers to confidently distinguish between peridot of different worlds.