FMF - Friends of Minerals Forum, discussion and message board

[Fiebre Verde]

This specimen is a good example of the material that can be found in Chivor.
Emeralds are shaped like long thin pencil leads and show a strong bluish cast.
Tiny nodules of crystallized pyrite can be seen in the close-up image.
Host rock is grey shale.

These combined characteristics leave little doubt about the origin of this specimen.

[Fiebre Verde]

Nice little aggregate of emeralds.

[Tobi]

GORGEOUS!!!

[Fiebre Verde]

Thanks Tobi!
For sure Colombia is a good source of fine beryls...

[Fiebre Verde]

At first glance this Muzo specimen does not look very appealing.
Just a couple of incomplete crystals perched on a dull calcite matrix (first image).
But as we get closer, some details start to sparkle.
Actually the round-shaped emerald on the edge of the specimen is a survivor - it has a true faceting grade!
Don't know how it escaped from the standard carnage. It might have been "protected" by a larger crystal nearby.

[Fiebre Verde]

The Polveros deposit has been known from the early 90’s, but it began producing commercial quantities only in the late 90’s.
This specimen is from the early production of this locality. It's a good example of the fine calcite crystals associated to the emeralds that comes out from the La Pita district.
The last 5 images look very much similar - I just could not resist!
Host rock is black shale.

[Fiebre Verde]

What makes this specimen interesting is... a broken crystal.
Due to pressure, crystal has broken into two almost equal parts, orthogonally to the c-axis.
Following this phase, the thermochemical conditions were favorable for a recrystallization of the discontinuity surfaces.
The upper half of the crystal is contacted.

[Tobi]

For sure one of the most aesthetic "damaged" mineral specimens ever ;-)

[Fiebre Verde]

[Fiebre Verde]

Emerald and quartz nicely perched on a large calcite rhomb.
There are a few patches of non-crystallized pyrite on the black shale host rock (not featured in the images).

[Fiebre Verde]

Some emeralds are valued for their internal "fire".
This one could fall in this category as the top 3 mm is literally on fire.
This is the direct result of a fracture which runs across the entire prism perpendicularly to the c-axis and reflects most of the light.
The crystals have a strong bluish cast and are striated parallel to the c-axis, a feature I have only seen in Chivor emeralds.
But the most striking feature is the basal pinacoid termination which has very complex crystallization patterns. These rugged markings on the C-face combined with the reflected beam produces a stunning visual effect.

Host rock is black shale coated with an aggregate of white albite (variety cleavelandite).

[Fiebre Verde]

Another example of the typical material which can be found in Chivor.
The white material is calcite and the host rock is black shale.

The rather saturated main emerald crystal is literally pinched by pyrite.
Note the linear markings parallel to the c-axis all over the prism faces.
Are these features directly related to the crystal growth process or are they related to a dissolution mechanism?
Growth or dissolution or ... else? Am a bit puzzled...

[Fiebre Verde]

The Muzo/La Pita deposits are not only known for their quality emeralds.
This specimen is a good example of the orange-brown parisite that can be found in these districts.
Although parasite is a rare mineral, it is relatively common in the Muzo/La Pita districts.
This is where parisite was discovered first in 1835 by J.J. Paris, former leaseholder of the Muzo deposits in the early part of the 19th century.
The crystals are double hexagonal pyramids, with or without the base.

The emerald prism shape is unusual - the base is slightly wider than the top.
This feature is only observed in La Pita where the famous "botellas" (bottle-shape) crystals are found.
The emerald crystal is translucent and nearly inclusion-free.

Host rock is black shale.

[Fiebre Verde]

Aesthetic specimen with calcite from Muzo.

[Fiebre Verde]

A very rough rock from Chivor
The matrix is composed by interlaced fine-grained and coarse-grained limestone mixed with pyrite and calcite.
The rock is big enough to host more little cavities but I wouldn't dare to break it apart.
Unusual material.

[Tobi]

It's such a wide variety of specimens from the Colombian emerald mines that we get to know through your work here, thanks again! How many emerald specimens do you possess overall?! ;-)

Tobi

[Fiebre Verde]

[Fiebre Verde]

Different world from the previous specimen (Chivor #83).
Massive piece of black shale coated with light gray and light brown calcite.
This is common material from the western belt.

I was told this specimen was from Muzo but it could as well be from Coscuez where elongated crystals are more commonly found.

A good discussion on the characteristics of the Muzo/Coscuez emeralds can be found in "Oppenheim, V. (1948): The Muzo Emerald Zone, Colombia, S. A; Economic Geology, Volume 43, pages 31-38."

[Fiebre Verde]

The overwhelming brownish hue is caused by iron oxide.
Even the original black shale host rock is oxidized.
Color of the beryl crystals tend toward a bluer green.
The black shale is coated by a 5mm thick layer of oxidized albite aggregate.
This specimen has a few interesting features which I have commented below.

[Fiebre Verde]

Aesthetic specimen from Coscuez.
Matrix in white marble-like calcite which produces a glistening effect all over the specimen.
Translucent and dark gray calcite crystals accompany the grass green emeralds.
There is a beryl crystal of the same size on each side of the specimen.