| Stilpnomelane | |
| Category: | Phyllosilicates Smectite group |
| Imasymbol: | Stp[1] |
| Strunz: | 9.EG.40 |
| System: | Triclinic |
| Class: | Pinacoidal (same H-M symbol) |
| Symmetry: | P |
| Unit Cell: | a = 21.72 Å, b = 21.72 Å c = 17.4 Å; α = 124.14° β = 95.86°, γ = 120°; Z = 6 |
| Color: | Black, greenish black, yellowish bronze, greenish bronze |
| Habit: | Platey, scaly and fibrous with comb structures; radiating groups |
| Cleavage: | Perfect on, imperfect on |
| Tenacity: | Brittle |
| Mohs: | 3–4 |
| Luster: | Vitreous to dull |
| Streak: | Gray white |
| Diaphaneity: | Subtranslucent to opaque |
| Gravity: | 2.77 – 2.96 |
| Opticalprop: | Biaxial (−) |
| Refractive: | nα = 1.543 – 1.634 nβ = 1.576 – 1.745 nγ = 1.576 – 1.745 |
| Birefringence: | δ = 0.033 – 0.111 |
| Pleochroism: | X: bright golden yellow to pale yellowY and Z: deep reddish brown, to deep green to nearly black |
| 2V: | 0–40 measured |
| Dispersion: | None |
| References: | [2] [3] [4] |
Stilpnomelane is a phyllosilicate mineral. It has the chemical formula .[4]
Stilpnomelane occurs associated with banded iron formations. It is a metamorphic mineral associated with the blueschist and greenschist facies.[2]
It was first described in 1827 for an occurrence in Moravia in the Czech Republic. The name is derived from the Greek for shining, and for black.[3]