silicates
Crocidolite
- Also known as
- blue asbestos
- Crystal system
- monoclinic
- Hardness
- 4 on the Mohs scale
- Lustre
- silky
- Colour
- Blue to blue-grey, fibrous
- Where it forms
- In banded ironstone formations, as fibrous seams within the layered rock.
- Chiefly from
- Northern Cape, South AfricaWestern AustraliaBolivia
Why it is that colour
Iron. It is the asbestiform variety of the amphibole riebeckite, and its fibres are fine, straight and sharp.
Safety
This is blue asbestos, and it is the most dangerous form of asbestos there is. Its fibres are thin enough to reach the deepest parts of the lung and durable enough to stay there for decades, and it is strongly associated with mesothelioma, a cancer with no cure and a latency of thirty to forty years. It is banned in most countries. Raw fibrous material should not be handled, disturbed, cut or kept, and if a specimen is suspected to be crocidolite the correct response is to seal it and consult local hazardous-waste guidance.
Where it comes from
Mined in South Africa’s Northern Cape and at Wittenoom in Western Australia. Wittenoom is the most consequential industrial disaster in Australian history: the town has been degazetted, removed from maps and closed off, and the death toll from Wittenoom-related mesothelioma and asbestosis runs to well over two thousand and is still rising.
Historical use
Used for insulation, fireproofing and cement products through the twentieth century, valued precisely for its durability and heat resistance.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
Worth knowing
Crocidolite is in this collection for one reason: it is the parent of tiger's eye. The pleasant golden stone sold everywhere formed by silica replacing this material fibre by fibre, and the two come from the same rocks in the same part of South Africa.
The finished stone is safe — the asbestos has been replaced. The rock it came from was not, and the Northern Cape and Wittenoom both carry the consequences. Wittenoom in Western Australia was officially erased: degazetted in 2007, power disconnected, name removed from road signs and maps, and the surrounding area declared a contaminated site covering roughly fifty thousand hectares.
It is worth holding both facts together. A material can be genuinely inert in one form and lethal in another, and the difference is not visible.
Identity checked against IMA-CNMNC master list, June 2025.