Natural bismuth vanadate from the Mutala pegmatite area,Mozambique

Bismuth vanadate (microprobe test) in varying shades of orange color and in well developed crystals (averaging 0.2 mm in size) occurs in bismutite in the Mutala granite pegmatite area, district of Zambezia, Mozambique. Two modifications of BiVO ₄were identified. An orthorhombic form is identical with pucherite and shows a₀ = 5.33₆ Å, b₀ = 5.05₃ Å, c ₀ = 12.02₁ Å. The crystal habit ranges from platy to stout prismatic. The X-ray powder pattern of the monoclinic form matches that of the synthetic monoclinic Bi-orthovanadate with a ₀ = 5.20₅ Å, b ₀ = 11.71₈ Å, c ₀ = 5.09₈ Å, = 90° 25. The crystal habit resembles that of a pyramidal scheelite crystal with the b-axis corresponding to the scheelite c-axis. Multiple twinning is seen on (101), in some instances with a composition plane (010).