FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Hello,
Here is a crystal of vorobyevite, a very rare variety of beryl.
The locality is Lipovka mine (Lipovskaya mine; Lipovka pegmatite field, Rezh district, Central Urals, Ural region, Russia.
Beryl is well known to enthusiasts and especially gemologists.
Beryl is a cyclosilicate : [Si6O18]12-. Simple 6-membered cycles.

The vorobyevite habit is tabular (pinacoid {0001}).
It is similar to that of morganite, another variety of beryl.
• emerald, green because of the presence of chromium;
• aquamarine, blue and green-blue (Fe2+);
• heliodor, golden or yellow-green because of the presence of iron 3+;
• morganite, pink to orange, containing lithium and cesium;
• goshenite, colorless;
• red beryl (bixbite), deep currant red, rich in manganese.
In their state of purity, they are all remarkable gems. Their hardness is great and also their cohesion. They do not present any cleavages.
Despite this, they accept (or tolerate) the inclusion of some foreign ions or molecules.
To these 6 varieties, we must add the extremely rare vorobyevite but already known by A. Lacroix (1922): Mineralogy of Madagascar.
The crystal habit of beryl is the prism more or less elongated along the senary axis.
Morganite is an exception because of the presence of cesium, although limited.
Morganite habit is rather tabular on the pinacoid {0001}.
The same goes for vorobyevite, alkali rich (K+).
Even if the type of insertion is different, the steric hindrance of these large atoms deforms the beryl lattice, without destroying it as pezzotaite does (~15% Cs). Vertical growth is disadvantaged compared to horizontal expansion.

PS: I was able to acquire a very small vorobyevite crystal which surprised me. Its Afghan origin causes the blue tint.
It appears to me in fact to be made up of a tabular vorobyevite crystal (pinacoid {0001} partly supporting a growth with parallel axes of small prisms stretched along the c axis (not vorobyevite).
My interpretation is as follows :
The first crystallization took place in a medium rich in alkalis-K+.
After stopping growth, a second crystallization resumes in an environment depleted in alkalis or with alkalis-Na+. Then the usual beryl habit stretched along the hexagonal axis can be imposed.
What do you think about ?

[Bob Carnein]

On Mindat, this is listed as not an approved mineral species. It seems to crop up periodically. I have a specimen and have labeled it "alkali beryl". Is this acceptable?

[Riccardo Modanesi]

Hi to everybody!
Vorobyevite is NOT a mineral species, but a variety of beryl, like aquamarine, emerald, morganite etc! Varieties are NOT species!
Greetings from Italy by Riccardo.