Evaluation of the Gemological Properties of Datolites from the Campotrera Deposit in the Northern Apennines (Italy)

Abstract

This work investigates the gemological properties of the datolite from the famous field of Campotrera near Reggio Emilia in Italy, for a possible commercial use in the market. This mineral occurs in widespread multi-centimeter veins, together with calcite and prehnite, within polygenic breccias in basaltic ophiolites. The most common form for this datolite is the double wedge with a prism (110) and a pinacoid (001). The gems obtained are mixed or carré cut, colorless or salmon pink, transparent, with a vitreous luster and weight between 1 to 5 carats. They have high brilliance, transparency and birefringence, glassy luster, absence of cleavage. The major chromophore is probably Fe, which occurs as inclusion of hematite and ilmenite. Raman investigations highlighted different fluid inclusions. The primary are randomly distributed or, in some cases, follow the growth zones, while the secondary form aligned tracks along the microcracks. Fluid inclusions can be biphasic and made up by liquid + gas (L + G), generally >10 mm in size, and more rarely, monophasic, composed only by liquid (L) generally <10 mm. The gems extracted from the rough sample are very valuable but their delicacy requires attention in the cutting and preparation of the jewels.