5.81 ct ULVOSPINEL IN BLACK OBSIDIAN – MADAGASCAR

Ulvöspinel in Black Obsidian (Back and White Image)

Ulvöspinel in Black Obsidian represents the “hidden-magnetic” anomaly of the volcanic world. A titanium-iron oxide trapped within a “glassy” silica matrix, it is a species I have always respected for its “steely-metallic” saturation and its status as a rare indicator of extreme volcanic cooling environments. For the specialist, a top-tier specimen from Madagascar is a prize of elemental sequestration; it offers a sub-metallic to vitreous luster and a “solid” presence that makes it a true “high-density” asset for the systematic vault. As an artist, I find the “starry-night” contrast of these metallic micro-crystals suspended in “ink-black” volcanic glass to be one of nature’s most sophisticated and “cosmic” palettes.

The Heritage & Discovery

Historical Significance: Ulvöspinel is a vital species for understanding the solid-solution series between Magnetite and titanium-rich oxides. Historically, it was named after the Ulvö Islands in Sweden, but the discovery of gem-grade “matrix” specimens in Madagascar has redefined the aesthetic standard for the species. In the world of fine minerals, it is celebrated for its natural, “magnetic-neon” pigment, which stands as a symbol of structural integrity. It serves as a reminder that the most “brilliant” displays in mineralogy often occur at the microscopic level, where trace amounts of Titanium ($Ti$) create a crystalline perfection within the chaos of cooling lava.

Discovery: The mineral was formally recognized as an inverse spinel structure where titanium and iron occupy specific lattice sites. Scientifically, it is a high-temperature oxide. Its discovery in the Androy region of Southern Madagascar provided mineralogists with the first clear look at the species’ potential for “sharp” inclusion-driven perfection within a rare location. My own respect for this material grew from observing its “sub-surface” flash; specifically, when the obsidian is polished, the Ulvöspinel inclusions create a “metallic-rain” effect that is unmistakable to the trained eye.

Important Mines: The undisputed world capital for the finest, “inclusion-rich” Black Obsidian with Ulvöspinel is the Ambovombe District in Androy, Madagascar. These Malagasy specimens set the global benchmark for color contrast and “micro-geometric” architecture. I also have a high regard for the classic finds from the Bushveld Complex in South Africa. For the vault, I prioritize the Madagascar material for its unmatched “void-black” depth and its status as a rare-location masterpiece of volcanic history.

Mineralogical Profile

Description: Ulvöspinel is a titanium iron oxide that crystallizes in the isometric (cubic) system, while the Obsidian matrix is an amorphous volcanic glass. The Ulvöspinel sits at a 5.5 to 6 on the Mohs scale, and the Obsidian sits at a 5 to 5.5. It is characterized by its sub-metallic to vitreous luster and its unmistakable, “obsidian-black to metallic-grey” color palette.

One of its most identifying traits is its strong magnetic response and its tendency to form minute octahedral crystals within the glass. It has a high refractive index (n approx 2.3 to 2.4 for the spinel) and a specific gravity (SG approx 4.7 to 4.8 for the spinel, 2.4 for the obsidian). Because it forms in rapidly cooling silicic lavas, it is often found in association with Magnetite, Ilmenite, and Feldspar. When I select a piece for the collection, I look for “even” distribution of the metallic inclusions and a “mirror-black” polish, as these highlight the sophisticated, three-dimensional geometry of the mineral’s growth. It is a dense, high-vibration mineral that offers a unique, “volcanic-neon” beauty unlike any other oxide-silica species.

Chemical Formula: Fe₂TiO₄ in SiO₂