A new mineral species, scottyite, ideally BaCu2Si2O7, has been found in the Wessels mine, Kalahari Manganese Fields, Northern Cape Province, South Africa. The mineral appears to have formed as a result of a hydrothermal event and is associated with wesselsite, pectolite, richterite, sugilite, and lavinskyite. Scottyite forms blocky grains with striations parallel to the c axis. Crystals are found up to 0.4 x 0.3 x 0.3 mm. No twinning is observed. The mineral is dark-blue in transmitted and under incident lights, transparent with pale blue streak and vitreous luster. It is brittle and has a Mohs hardness of 4~5; cleavage is perfect on {100} and {010} and no parting was observed. The calculated density is 4.654 g/cm3. Optically, scottyite is biaxial (-), with α = 1.750(1), ß = 1.761(1), and γ = 1.765(1), 2Vmeas = 66(2)°. It is insoluble in water, acetone, or hydrochloric acid. An electron microprobe analysis produced an average composition (wt%) (8 points) of CuO 36.98(31), BaO 35.12(16), SiO2 27.01(61), SrO 0.28(5), and Na2O 0.06(2), and total = 99.45(65), yielding an empirical formula (based on 7 O apfu) Ba1.00Sr0.01Na0.01Cu2.04Si1.97O7.

Scottyite is the natural analog of synthetic BaCu2(Si,Ge)2O7, which exhibits novel one-dimensional quantum spin-1/2 antiferromagnetic properties with tunable super-exchange interactions. It is ortho-rhombic, with space group Pnma and unit-cell parameters a = 6.8556(2), b = 13.1725(2), c = 6.8901(1) Å, and V = 622.21(6) Å3. The structure of scottyite is characterized by flattened CuO4 tetrahedra sharing corners with one another to form chains parallel to the c axis. These chains are interlinked by Si2O7 tetrahedral dimers and Ba2+. The Ba2+ cations are bonded to seven O atoms in an irregular coordination. The average Si-O, Cu-O, and Ba-O bond lengths are 1.630, 1.941, and 2.825 Å, respectively. Scottyite is topologically related to a group of compounds with the general formula BaM2+2Si2O7, where M = Be (barylite and clinobarylite), Fe (andrémeyerite), Mg, Mn, Co, and Zn.

You do not have access to this content, please speak to your institutional administrator if you feel you should have access.