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[Roger Warin]

I suggest the signification of an old French name.
The specimen (galena) will be presented in Cesàro’s part.

Minerals are often on a crystallized matrix to which no one pays much attention. Ancient mineralogists gave a generic term for all these small rhombohedral crystals: the French term was spath perlé (pearl spar), perhaps because of small reflections of rug.
Mindat defines this term as dolomite.
In fact, a careful reading of an old label provides the answer as a Rosetta Stone.
The pearl spar is essentially rhombohedra of dolomite, ankerite and siderite (calcite is easily recognized).

Here is the translation of the French label, written around 1890 :

Galène # 3296 – Freiberg, Saxe.
p a1 a7/4 {001}, {111}, {744}.
The substance crystallized in pearl rhombohedra is ankerite or siderite, as it browns very with blowlamp;
after the action of fire, it is painfully magnetic;
So probably this is ankerite.

p a1 + a trapezohedron neighbor of a2;
it makes an angle of about 16 ° → a7/4.
(theoretically this angle is 15.8 °)

Note: pearl spar is not only dolomite as Mindat said.
Roger.

[Andreas Gerstenberg]

You´re right there, it´s not always dolomite. However, it depends on the locality. Nearly all pearl spar samples from Annaberg/Saxony are dolomite. There Freiberg specimens could be ankerite or dolomite (or mixed crystals).

The name was created by Abraham Gottlob Werner ("Perlspat"), indeed due to the white and silky colour.