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The Mineral olmiite

Pink-Beige Olmiite Balls

Olmiite is a relatively new mineral, only being officially named as a new species by the IMA in 2006. To date, it is found only in the Kalahari Manganese Field of South Africa. It is unusual for a newly discovered mineral to form is such large and excellent examples, with many well-formed and highly aesthetic examples of this mineral.

Olmiite forms a solid solution series with the much rarer mineral Poldervaartite. Many specimens that had been labelled as Poldervaartite have in fact been Olmiite upon analysis. Olmiite is named after Filippo Olmi, an Italian mineralogist from Florence, Italy.

Chemical Formula

CaMn[SiO₃(OH)](OH)

Color

Pale yellow, tan, orange-brown, orange, peach, pink, light red, grayish-pink, light gray

Crystal System

Orthorhombic

Properties

Streak
White

Hardness
5 - 5.5

Transparency
Transparent to nearly opaque

Specific Gravity
3.0 - 3.1

Luster
Vitreous, pearly

Cleavage
None

Fracture
Uneven

Tenacity
Brittle

Other ID Marks
May be fluorescent red in shortwave ultraviolet light.

Crystal Habits

In radiating spheres, as botryoidal, acicular, and wheat sheaf crystal groups, in groups of ball-shaped aggregates, and in stacked crystal plates. Individual pyramidal crystals are uncommon.

Additional Information

Composition
Basic calcium manganese silicate

In Group
Silicates; Nesosilicates

Striking Features
Color, crystal habits, and locality

Environment
In manganese-rich hydrothermal replacement deposits.

Rock Type
Metamorphic

Uses

Well formed Olmiite examples with good color and form are highly valued by mineral collectors.

Noteworthy Localities

Olmiite has only been found in the Kalahari Manganese Field of South Africa, where it has been found both at the N'Chwaning Mines in Kuruman and the Wessels Mine in Hotazel.