2.33 ct ENDLICHITE – MOROCCO

Endlichite

Endlichite is a gemstone that represents a rare chemical bridge within the apatite supergroup. A variety of Vanadinite, it is distinguished by its high arsenic content, which pushes the traditional fiery red of Vanadinite into a more sophisticated, “antique” palette. I have always been fascinated by its unique coloration—ranging from a rich honey-yellow to a deep, “cognac” brown or olive-green. It typically forms as sharp, hexagonal prisms that possess a sub-adamantine to resinous luster, giving the crystals a heavy, “metallic-glass” appearance. To find gem-quality Endlichite is a true specialist’s hunt; it is a stone of structural transition, sitting perfectly between Vanadinite and Mimetite. For the collector, it offers a refined, earthy elegance that is far more elusive than its bright red cousins.

The Heritage & Discovery

Historical Significance: Endlichite is a vital mineral for understanding the chemical “substitution” that occurs in the oxidation zones of lead deposits. Historically, it was identified as a specific intermediate member of the Vanadinite-Mimetite series, where arsenic replaces a significant portion of the vanadium. In the world of fine minerals, it is celebrated for its unusual crystal habits—often appearing as elongated, “acicular” needles or robust, “barrel-shaped” prisms. It stands as a symbol of the mineralogical “middle ground,” bridging the gap between the vanadium-rich reds and the arsenic-rich yellows of the pyromorphite-mimetite group.

Discovery: The mineral was first described in 1885 and was named in honor of Frederic Miller Endlich (1851–1899), an American geologist and mineralogist who was instrumental in the early surveys of the American West. The type-locality is the Lake Valley District in New Mexico, USA. Its discovery provided mineralogists with the first clear evidence of a complete solid-solution series between Vanadinite and Mimetite, fundamentally changing how we classify these lead-based minerals.

Important Mines: The legendary source for world-class Endlichite is the Hillsboro and Lake Valley districts in New Mexico, USA. These mines produced the iconic, large, “butterscotch” colored crystals that defined the species. I also have a high regard for the spectacular specimens found in the Touissit Mine in Morocco, which often show incredible luster and transparency. For the vault, I prioritize the New Mexican material for its historical pedigree and the Moroccan pieces for their exceptional, “gemmy” brilliance.

Mineralogical Profile

Description: Endlichite is an arsenic-rich variety of Vanadinite (lead chloro-vanadate) that crystallizes in the hexagonal system. It sits at a 2.5 to 3 on the Mohs scale, making it a delicate mineral that must be protected from abrasion and handled with care. It is characterized by its high density and its sub-adamantine to resinous luster.

One of its most identifying traits is its chemical transition. Because it contains both arsenic and vanadium, its color is often zoned, showing shifts from yellow to brown within a single crystal. It has a high refractive index ($n \approx 2.1$ to $2.3$), which provides a brilliant, “snappy” reflection even in darker specimens. It is a very heavy mineral, with a specific gravity of approximately $6.7$ to $7.1$. When I select a piece for the collection, I look for “sharp” hexagonal terminations and a high-gloss luster, as these highlight the sophisticated, three-dimensional geometry that makes Endlichite a standout for the systematic collector. It is a dense, grounding mineral that offers a unique, “old-world” beauty unlike any other lead species.

Chemical Formula: Pb₅([V,As]O₄)₃Cl