Rhodochrosite is a mineral that has long captivated collectors, geologists, and gemologists alike for its striking colors. A manganese carbonate mineral (MnCO₃), it is renowned for its vibrant shades of pink and red. While rhodochrosite is found in many parts of the world, the Kalahari Manganese Fields of South Africa stand out as one of the most significant sources globally, although Collectors Edge in the States may argue that point (And yes, the Alma Rose is impressive, but, you know, it’s not N’chanting, heh)

Overview of the Kalahari Manganese Fields

While this isn’t the first article I’ve written about the Kalahari Manganese Fields, it is my first time focusing on a specific mineral—rhodochrosite—so I’ll keep things concise.

The Kalahari Manganese Fields stretch over an impressive area of about 350 kilometers in length and 100 kilometers in width, primarily situated around Hotazel, with extensions into the Wessels and Mamatwan regions. These manganese ore bodies were first discovered in the early 20th century, and since then, they have become one of the world’s most vital sources of manganese.

Mineralization in the area is dominated by manganese oxide minerals embedded within the Palaeoproterozoic Hotazel Formation, which dates back approximately 2.2 billion years. This formation forms part of the Transvaal Supergroup, where manganese ore is layered between banded iron formations and carbonate deposits. Over its extensive geological history, the Kalahari Manganese Fields have undergone numerous geological processes, including uplift, deformation, folding, thrusting, and alterations from both hydrothermal and supergene influences.

While the original manganese ore remains the primary focus for mining, it was the later “Wessels-event” that led to the formation of some of the rarest and most exotic minerals that have brought global attention to the Kalahari Manganese Fields, particularly among mineral collectors.

For context, the Wessels-event refers to the hydrothermal alteration of primary manganese ore, particularly those mined at Wessels Mine. This event not only altered the chemical and physical properties of the manganese deposits but also gave rise to several unique and rare mineral species. Wessels Mine, in particular, has produced numerous type specimens, including minerals like vonbezingite, effenbergerite, poldervaartite, and wesselsite. These minerals remain exclusive to the Kalahari Manganese Fields, adding to the area’s reputation for mineralogical diversity.

However, while rhodochrosite is present in association with these older manganese ores, it is the later, hydrothermally-altered rhodochrosite from N’Chwaning I and II mines that is truly spectacular, both in terms of crystal size and beauty.

Rhodochrosite from N’Chwaning

Rhodochrosite was first officially recorded in 1963 from the Hotazel opencast mine. Early specimens were relatively modest and consisted mainly of drusy rhodochrosite associated with gypsum. By 1967, a few scalenohedral crystals began to emerge from Hotazel, but it wasn’t until a decade later, with the development of N’Chwaning I mine, that a significant and remarkable discovery was made. This discovery unveiled a stunning variety of colors and crystal forms, from wine-red to pale-pink hues, and a wide range of shapes, including sharp scalenohedral “dog-tooth” crystals, smooth rounded spheres, and delicate “wheat-sheaf” bundles of crystals. The latter form, in particular, is now one of the rarest and most prized forms for collectors.

As N’Chwaning I mine’s shaft deepened, it penetrated several pockets filled with beautiful rhodochrosite crystals. This led to the discovery of hundreds of loose specimens, many of which now reside in top-tier mineral collections and museums around the world.

Undamaged rhodochrosite crystals remain somewhat rare. The scalenohedral crystals, in particular, are fragile, with their terminations prone to cleaving.

Typical associations for rhodochrosite from the N’Chwaning mines include minerals such as manganite, gypsum, todorokite, chalcedony, and drusy quartz, the latter often coating the characteristic “dog-tooth” rhodochrosite.

Geologically, the formation of rhodochrosite in the Kalahari Manganese Fields is tied to relatively recent events, distinct from the older Wessels-type alteration process that occurred more than a billion years ago.

Older rhodochrosite found in both N’Chwaning and Wessels mines—linked to the ancient Wessels-event—tends to be less visually spectacular. These older crystals are generally smaller, pink rhombohedral forms, usually less than a centimeter in size, and sometimes found with other rare minerals like gageite, orlymanite, caryopilite, and leucophoenicite.