Probertita
Probertita is a mineral with formula NaCa(B₅O₉)·5H₂O, in the Boratos group. This specimen comes from Kohnstein Quarry, Niedersachswerfen, Nordhausen, Turingia, Alemania and joined the Terrium collection in 2025.
Description
Ice needle. Completely transparent prismatic crystal, with well-defined faces and an elongated habit. Its extreme lightness (0.01 g) and absolute transparency give it an ethereal, minimalist air. Shows a slight pale green response under UV light.
About Probertita
Probertite is a rare hydrated sodium–calcium borate, first described in 1883 in California. It usually occurs as prismatic, colourless to white crystals; most known specimens from California—its type locality—and Turkey form dense aggregates of elongated prisms, ranging from translucent to opaque. Specimens from Kohnstein stand out for the opposite: transparent, cleaner crystals that are visually much finer.
About the locality
A classic but low-yield locality. Its 20th-century history adds a harsh context: the Kohnstein galleries were incorporated into the Mittelwerk underground factory, linked to the German V-2 rocket programme. For borate collectors it is one of the world’s reference localities for high-quality probertite.
Technical data
- Catalogue No.
- 0175
- Composition
- NaCa(B₅O₉)·5H₂O
- Name
- Probertita
- Group
- Boratos
- Category
- Estélites
- Mine
- Kohnstein Quarry
- District / Municipality
- Niedersachswerfen, Nordhausen
- Province
- Turingia
- Country
- Alemania
- Size (cm)
- 6.2 x 0.6 x 0.6
- Weight
- 0.01 g
- Acquired
- 2025
- Etymology
- Named after Frank H. Probert (1850–1920), an American chemist.
- Quality
- Buena
- Value trend
- Estable
Related specimens
- Arsénico (Nativo) — Alemania
- Autunita — Alemania
- Estroncianita — Alemania
- Hematites (Especularita Azul) — Alemania
- Natrozippeita — Alemania
- Plata (Filiforme) — Alemania
- Uraninita (Pechblenda) — Alemania
- Uranocircita — Alemania