10 of 15 in the register · Blue · Ravenholme Vein · 11 February 2025
Azurite
Cu₃(CO₃)₂(OH)₂ · Mohs 3.5 – 4
The only blue in the register, and the last entry on the circle before it runs out of colours entirely.
| Body colour | deep blue, glassy |
|---|---|
| Streak | pale blue |
| Measured | #77a1dc |
| Deposit | 95.16% |
| Lightness | 65.54 |
| Chroma | 34.02 |
| Hue | 272.0° |
| Hardness | 3.5 – 4 |
| Locality | Ravenholme Vein |
| Written | 11 February 2025 |
Blocky crystals of a deep ultramarine crusted on rough pale rock, with one face flat enough to throw the light back. Azurite and malachite are the same copper, the same carbonate, the same vein and different amounts of water; azurite is the drier of the two and it turns into malachite slowly if it is left where it can get at any. Half the specimens in the world that were collected as azurite have gone green at the edges.
The streak is a light, slightly greyed blue at 272°, and it is the last entry on the circle. After it the register runs out of hue altogether — four powders with a lightness and no direction, and then one with neither. It is a strange place for the colour sequence of a whole collection to stop, and it is not a stylistic decision: it is the fact that mineral powders in this district go red, brown, yellow, green, blue, and then nothing.
Ground fine, azurite is the pigment that used to be called mountain blue, and it was expensive in the way lapis was expensive and for the same reason — there was no synthetic alternative until there was, at which point the trade in it stopped in about a decade. The powder on this plate is the same substance, at rather less than the same value.
Its chroma is 34, which is high enough that its position is not in doubt, and it is the only entry between 136° and 24° going the long way round. Everything the site is printed on sits in that stretch behind it.