Calcite

Calcite is a carbonate mineral and the most stable form of calcium carbonate; its hardness of 3 is a reference point on the Mohs scale, per Wikipedia. It is typically colourless or creamy white with brownish shades, and a transparent form is used for optical purposes. Hall lists it in green, blue, yellow, orange, clear, brown, pink, grey and red, and calls it an amplifier and cleanser of energy that she links to psychic abilities, a calm mind and memory. Cunningham says its energy, planet and element vary with colour, and lists its powers as spirituality, centring, peace, love, healing, purification, money, protection and energy; he says its double refraction is used in spells to strengthen a rite twofold. The coloured sorts are separate ingredients. All uses are the authors' claims.