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[Fiebre Verde]

Elongated crystal from Chivor with a complex termination.

Crystal has an unusual hollow cavity down through the upper quarter (5mm).
The void inside the crystal looks like a real crystal - so this is clearly a negative crystal.

The cause of this negative-crystal cavity (crystal-shaped hollow cavity) is unclear to me.
Schmetzer & al. (2011), Chemical and growth zoning in trapiche tourmaline from Zambia – a re-evaluation, JoG, Vol 32, No.5-8
suggest 2 possibilities
1) Trapping of a solid inclusion and subsequent blocking of crystal growth with the formation of a growth induced, elongated void in the direction of crystal growth (arrow) subsequent to trapping of the small mineral grain
2) Trapping of a solid inclusion, movement of the trapped small mineral grain in the direction of the arrow and of the growing crystal face and formation of a growth induced, elongated void in the wake of the moving mineral grain, a mechanism repeated in several steps

Are any of you aware of any other possible explanation?

[Roger Warin]

Hi Fiebre Verde,
You said “The cause of this crystal-shaped hollow cavity is unclear to me.”

I think it would be a fluid inclusion, a liquid with maybe even a third gaseous phase (CO2 ?), which has locally prohibited growth (in hydrothermal conditions).
Under these conditions, the crystal grows by forming faces whose indices are consistent with inverted growth.
Subsequently, fluid inclusion escaped.
A solid inclusion would give foreign faces to beryl and would have dropped impurities, I believe.

[Fiebre Verde]

[Roger Warin]

OK, thank you Gerard.
Roger.

[Roger Warin]

Hi Gérard,
Summer nights may be good for insomnia.
Why not think about minerals?
I compared the presence of a cavity in your emerald to the texture of the beryl variety heliodor of Ukraine.
These negative facets are not growth figures, but on the contrary they result from an inverse process, namely dissolution in a hydrothermal medium at the end of growth.
The kinetics of this dissolution depends on the population density of the reticular planes.
These figures are not in relief, but in negative, as in an intaglio. These are hoppers (stairs cavities).

[Fiebre Verde]

[Fiebre Verde]

Beryl prism solidly attached to a calcite crystal.
Dissolution patterns can be seen on all faces.

[Fiebre Verde]

Lustrous dolomite, calcite, pyrite, on black shale.

[Fiebre Verde]

Semi-transparent double terminated crystal which exhibits many internal cracks and fractures.

[Fiebre Verde]

Aggregate of double terminated crystals.
The white calcite, the clear quartz, the small pyrite nodules, and the crumbly grey shale are all in the back of the aggregate (not seen in the photo).

[Fiebre Verde]

Group of 10+ grass green crystals.
Host rock is a bedded limestone.

[Fiebre Verde]

Beryl crystal partly encapsulated in a calcite shell.
Host rock is black shale.

[Fiebre Verde]

Small beryl crystal has grown on top of the large one.

[Fiebre Verde]

Beryl crystal has a complex pyramidal termination.

[Tobi]

Just too good to be true! Especially the one with the "baby" crystal attached to its top - what a beauty!