Cristobalite in/on Obsidian

Item Description

An interesting lithophysae of stark black obsidian which plays host to light grey colored spherules of Cristobalite (a tetragonal polymorph of quartz) lining the interior. According to the entry in Alvaro's collection catalogue, he mentions that Cristobalite is a stable form of silica above (SiO2) between its melting point of 1,728° C (3,142° F) and 1,470° C (2,678° F). He also mentions that there are tiny crystals of the iron silicate Fayalite on the piece, and with a loupe I can see some TINY golden-brown colored spots, that are less than 1 mm, which could be the Fayalites. These pieces are notably rare, and I've only seen a few comparable specimens from various world localities in my life.
From the collection of the recently deceased Alvaro Lucio, arguably the most well-known and accomplished mineral dealer and collector in Brazil. Alvaro graduated with a degree in civil engineering, mining and metallurgy from the Escola de Minas de Ouro Preto in 1949. He began his PhD in the United States and completed it at the Federal University of Minas Gerais. He worked as a professor of extractive metallurgy at UFMG, and also as a technical consultant for several companies in the sector. He was the author of several works, published in books and magazines around the world. He received several honors for his contribution to the development of metallurgy and the introduction of metallurgical physical chemistry in Brazil. His knowledge, solicitousness and enthusiasm will be greatly missed in the mineral world.