TITANITE (SPHENE) with EPIDOTE, Capelinha Minas Gerais Brazil (small cabinet)

Titanite, also known as sphene, is a calcium titanium nesosilicate mineral with the chemical formula CaTiSiO5. It often contains trace amounts of iron and aluminum, along with rare earth elements such as cerium and yttrium. Additionally, thorium may partially substitute for calcium in its composition.

Epidote, with the chemical formula Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), is a mineral that crystallizes in the monoclinic system and is frequently found in well-formed crystals. These crystals typically exhibit a prismatic shape, with elongation occurring perpendicular to a single plane of symmetry. The term "Epidote" originates from the Greek word 'epidosis,' which translates to "increase," reflecting the characteristic of one side of the prism being longer than the other. The crystal faces are often marked by deep striations, and twinning is common. Variations in iron content influence several properties of the mineral, including color, optical constants, and specific gravity. Epidote can appear in shades of green, grey, brown, or nearly black, but it is most commonly recognized by its yellowish-green or pistachio-green hue. It exhibits strong pleochroism, displaying colors such as green, yellow, and brown. Clinozoisite, a related species, is typically green, white, or pale rose-red and contains minimal iron, sharing the same chemical composition as the orthorhombic mineral zoisite.

As a prevalent rock-forming mineral of secondary origin, epidote is primarily found in metamorphic rocks like marble and schist. It also forms through the hydrothermal alteration of various minerals, including feldspars, micas, pyroxenes, amphiboles, and garnets, within igneous rocks. A rock composed of quartz and epidote is referred to as epidosite. Notable localities for well-developed epidote crystals include Knappenwand near the Großvenediger in Salzburg, where dark green prismatic crystals are found in epidote schist alongside minerals such as asbestos and calcite. Other significant locations include the Ala Valley and Traversella in Piedmont, Arendal in Norway, Le Bourg-d'Oisans in Dauphiné, Haddam in Connecticut, and Prince of Wales Island in Alaska, where large, dark green tabular crystals can be observed.