Riebeckite is a silicate mineral. It is found in nature as both a fibrous form and a solid form. The fibrous form, called blue asbestos or crocidolite asbestos, is one of the six types of asbestos. It is considered by many experts to be the most dangerous type of asbestos. It can cause cancer and asbestosis. It was formerly used in Kent brand cigarettes as a filter material. It is rare in construction compared to white asbestos, but it is sometimes found in caulking, cement, wallboard, rope, and numerous other products. Due to its hazards, blue asbestos is no longer mined commercially.
Quick facts General, Category ...
| Riebeckite |
|---|
 Black riebeckite in an alkaline pegmatite from Lindinosa near Évisa, Corsica, France |
|
| Category | Silicate mineral |
|---|
Formula
(repeating unit) | ☐Na2(Fe2+3Fe3+2)Si8O22(OH)2 |
|---|
| Crystal symmetry | Monoclinic 2/m |
|---|
| Unit cell | a = 9.76 Å, b = 18.04 Å, c = 5.33 Å; β = 103.59°; Z=2 |
|---|
|
| Color | Black, dark blue; dark blue to yellow-green in thin section |
|---|
| Crystal habit | As prismatic crystals, commonly fibrous, asbestiform; earthy, massive |
|---|
| Crystal system | Monoclinic - Prismatic |
|---|
| Twinning | Simple or multiple twinning parallel to {100} |
|---|
| Cleavage | Perfect on {110}, intersecting at 56° and 124°; partings on {100} and {010} |
|---|
| Fracture | Conchoidal to uneven |
|---|
| Tenacity | Brittle |
|---|
| Mohs scale hardness | 6 |
|---|
| Luster | Vitreous to silky |
|---|
| Streak | Pale to bluish gray |
|---|
| Diaphaneity | Semitransparent |
|---|
| Specific gravity | 3.28–3.44 |
|---|
| Optical properties | Biaxial (-) |
|---|
| Refractive index | nα = 1.680–1.698 nβ = 1.683–1.700 nγ = 1.685–1.706 |
|---|
| Birefringence | δ = 0.005–0.008 |
|---|
| Pleochroism | X = blue, indigo; Y = yellowish green, yellow brown; Z = dark blue |
|---|
| 2V angle | Measured: 68° to 85°, Calculated: 62° to 78° |
|---|
| Dispersion | Strong |
|---|
| References | [1][2][3][4] |
|---|
Close
.jpg)