Journal Article

Marchettiite, (NH 4 )C 5 H 3 N 4 O 3 , a new organic mineral from Mount Cervandone, Devero Valley, Western–Central Alps, Italy

Lorenzetti, Alessandra, Nestola, Fabrizio, Ernst, Michelle, Zorzi, Federico, Lanza, Arianna, Guastoni, Alessandro, Gentile, Paolo, Andò, Sergio

2022

Overview

The new mineral marchettiite (IMA2017-066) is the natural equivalent of ammonium hydrogen urate. It has a simple molecular formula C 5 H 7 N 5 O 3 and can be alternatively written as (NH 4 )C 5 H 3 N 4 O 3 . Marchettiite was found in a cleft at Mount Cervandone, Devero Valley, Piedmont, Italy, where it occurs as aggregates of opaque pale pink to white, platy prismatic crystals. This mineral has a white streak, dull and opaque lustre, it is not fluorescent and has a hardness of 2–2.5 (Mohs’ scale). The tenacity is brittle and crystals have a good cleavage parallel to 001. The calculated density is 1.69 g/cm 3 . Marchettiite is biaxial (–) with 2V of 47.24°; the optical properties of marchettiite were determined by periodic-DFT methods providing the following values: α = 1.372, β = 1.681 and γ = 1.768. No twinning was observed. Electron microprobe analyses gave the following chemical formula: C 4.99 H 6.97 N 4.91 O 3.00 . Although the small crystal size did not allow refinement of structural data by single-crystal diffraction, we were able to refine the structure by powder micro X-ray diffraction. Marchettiite has space group P$\\bar{1}$and the following unit-cell parameters: a = 3.6533(2) Å, b = 10.2046(7) Å, c = 10.5837(7) Å, α = 113.809(5)°, β = 91.313(8)°, γ = 92.44(1)° and V = 360.312 Å 3 . The strongest lines in the powder diffraction pattern [ d in Å ( I )( hkl )] are: 9.784(50)(001); 8.663(80)(01$\\bar{1}$); 5.659(100)(011); 3.443(100)(10$\\bar{1}$); 3.241(70)(003) and 3.158(100)(1$\\bar{1}\\bar{1})$. Marchettiite is named after Gianfranco Marchetti, the mineral collector who found this mineral.