sapphirine

{{Infobox mineral | boxtextcolor= #FFFFFF | boxbgcolor = #172f5d | name = Sapphirine | category = Silicate mineral | image = Sapphirine-203257.jpg | caption = Indigo-blue sapphirine crystal from Ft. Dauphin, Madagascar (size: 2.1 x 1.9 x 1.4 cm) | formula = | IMAsymbol = Spr | strunz = 9.DH.45 | system = 2M polytype: monoclinic 1A polytype: triclinic | class = 2M polytype: prismatic (2/m) 1A polytype: pinacoidal () | symmetry = 1A polytype: P Other polytypes: 3A, 5A, 2M, 4M | unit cell = a = 11.27 Å, b = 14.4 Å c = 9.93 Å; β = 125.5°; Z = 4 | colour = Light to dark blue or green, white, gray, pale red, yellow | habit = Anhedral, granular, tabular | twinning = Uncommon on {001} | cleavage = Poor to indistinct on {100}, {001}, and {010} | fracture = Subconchoidal to uneven | mohs = 7.5 | lustre = Vitreous | refractive = nα = 1.701 – 1.729 nβ = 1.703 – 1.732 nγ = 1.705 – 1.734 | opticalprop = Biaxial (−) | birefringence = δ = 0.004 – 0.005 | 2V = Measured: 47 to 114° | pleochroism = X = colorless, pale reddish, yellowish green, pale yellow; Y = sky-blue, lavender-blue, bluish green; Z = blue, sapphire-blue, dark blue | streak = White | gravity = 3.40–3.58 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = }}

Sapphirine is a rare mineral, a silicate of magnesium and aluminium, with the chemical formula ( (with iron as a major impurity). Named for its sapphire-like colour, sapphirine is primarily of interest to researchers and collectors: well-formed crystals are treasured and occasionally cut into gemstones. Sapphirine has also been synthesized for experimental purposes via a hydrothermal process.