3.15 ct SENARMONTITE – ALGERIA

Senarmontite Senarmontite is a gemstone that exists in the rare, ethereal space of the "octahedral oxides." I have always found it to be a mineral of quiet, crystalline perfection; it forms as sharp, water-clear to pearly-gray octahedrons that look remarkably like colorless diamonds at first glance. It is an antimony oxide, and for the collector, it represents one of the most brilliant rarities in the world. Faceting Senarmontite is an exercise in extreme caution—it is incredibly soft and possesses a resinous to sub-adamantine luster that can be easily marred during the process. However, when you succeed, you are rewarded with a stone that has a high refractive index and a ghost-like, silvery brilliance. It is a gem for those who appreciate the delicate, geometric beauty of the oxidation zone, where harsh ores are transformed into transparent works of art. The Heritage & Discovery Historical Significance: Senarmontite is a classic secondary mineral, typically formed through the oxidation of Stibnite and other antimony-bearing ores. Historically, it has been studied alongside its polymorph, Valentinite, as they share the same chemistry but differ in crystal structure. It represents the "isometric" side of antimony oxidation—a snapshot of specific temperature and pressure conditions that favor the cubic system over the orthorhombic. In the world of rare gems, it is prized for its structural simplicity and its ability to form crystals of exceptional geometric clarity. Discovery: The mineral was first described in 1851 and was named in honor of Henri Hureau de Sénarmont (1808–1862), a distinguished French mineralogist and professor at the École des Mines in Paris. De Sénarmont was a pioneer in the artificial synthesis of minerals, and naming this elegant oxide after him was a tribute to his contributions to our understanding of crystal formation and optical properties. Important Mines: The world’s premier source for spectacular, large, and transparent Senarmontite crystals is the Djebel Hammimat Mine in Constantine, Algeria. This locality is legendary, producing the sharp octahedrons that are the gold standard for the species. I have also seen fine mineralogical specimens from the Quebradillas Mine in Durango, Mexico. For the vault, I prioritize the Algerian material, as the crystals from Djebel Hammimat possess a clarity and size that allow for the rare opportunity to facet a truly world-class, colorless collector's gem. Mineralogical Profile Description: Senarmontite is an antimony trioxide that crystallizes in the isometric (cubic) system. It sits at a 2 to 2.5 on the Mohs scale, making it one of the softest minerals we handle and strictly reserved for protected display or very specialized collections. It is characterized by its resinous to sub-adamantine luster and its colorless to pale gray appearance. One of its most identifying features is its habit; it almost always forms as perfect octahedrons, often with slightly stepped or skeletal faces. Despite its softness, it has a surprisingly high refractive index ($n \approx 2.09$), which gives faceted stones a brilliant, silvery "fire" that belies their delicate nature. Because it is an oxide of antimony, it is quite dense, a characteristic "heaviness" that collectors often notice when handling matrix specimens from Algeria. Chemical Formula: Sb₂O₃