Pezzottaite - Encyclopedia

    Class : Silicates
    Subclass : Cyclosilicates
    Crystal system : Trigonal
    Chemistry : Cs(Be₂Li)Al₂(Si₆O₁₈)
    Rarity : Very rare

Pezzottaite is a mineral belonging to the beryls group, rich in Cs and Li and raspberry pink in color. Named in honor of Doctor Federico Pezzotta (Natural History Museum of Milan), it was presented for the first time in 2003 at the Tuscon mineralogical exhibition, as the new pink beryl from the pegmatite of Sakavalana close to the small village of Ambatovita in Madagascar. Sakavalana pegmatite was exploited from 1940 for its polychrome tourmalines. In November 2002, miners uncovered a cavity containing numerous gemmy crystals, which were then sold in Antananarivo, the capital of Madagascar. Very quickly the pink color of these crystals reminiscent of tourmaline and their morphology, morganite (variety of beryl), sowed doubt in the minds. The first analyzes (carried out by F. Pezzotta) revealed that the mineral in question had high concentrations of cesium (Cs). In September 2003 the species was validated by the IMA under the name of pezzottaite. It is a rare mineral sought after by collectors that has been cut into gemstones.

In a classic beryl, the (hexagonal) structure is formed by rings of six silicon tetrahedra, stacked on top of each other along the c axis. They thus form channels which can be occupied by water or various alkalis such as Na (and Cs in small quantities). In the pezzottaite a large quantity of Cs occupies these same channels. Since Cs is an atom of large size, its abundant presence eventually deforms the crystallographic structure which then becomes trigonal. From an optical point of view, pezzottaite has a raspberry pink color, as well as an orange to purple dichroism, quite characteristic of the mineral when observed perpendicular to the c axis.

The coloring element, is a subject still much discussed with regard to the pezzottaite. Indeed, analyzes carried out on crystals from Burma show a high concentration of cesium in the most colored parts of the crystal. Similar analyzes were carried out on crystals from Madagascar, the type locality, and here it is the reverse some unstained areas presented concentrations of up to 19% (in percentage of oxides). So Cs does not seem to play a particular role in this raspberry-pink color. In reality it seems that Cs cannot play the role of a coloring element simply because it does not have electrons in the d-orbital (atomic orbital : space where it is probable to find an electron). There are suspicions about manganese which is known to be the coloring element of many minerals. However, let us not forget that in pezzottaïte, lithium is in abundance... To be continued...

Under the microscope, pezzottaite polarizes in yellowish-gray hues of the first order (in analyzed polarized light). Uniaxial negative, the mineral has a straight extinction along c as well as a birefringence close to 0.011 (np = 1.612 - 1.620, ng = 1.601 - 1.611). A figure which essentially depends on the quantity of Cs present in the crystal.

This mineral is not present in the French underground.

Pezzottaite has no twinned crystals known.

No scam known for this mineral.