O. v. Knorring

Cookeite from the Muiane pegmatite, Zambezia, Mozambique

This paper describes a cookeite occurring as large rosettes crystallized in an open vug in the Muiane granite pegmatite in Zambezia, Mozambique. Optical properties, chemical composition, X-ray powder pattern, single crystal data and infra-red absorption are given. The mineral represents a pseudo-hexagonal one-layer semi-random cookeite with noticeable contents of beryllium and boron.

Niobian wolframite from the Nuaparra pegmatite, Zambezia, Mozambique

Niobian wolframite is chemically an intermediate between wolframite and an iron-manganese niobate of the type FeNbO 4 . Single crystal X-ray photographs indicate systematic extinctions consistent with the monoclinic wolfaamite space group P2/c. a 0 =4.735 , b 0 =5.726 , c 0 =5.090 , β=90°. The mineral is opaque, in colour dark grey to almost black. Specific gravity 6.08. Hardness 5. No cleavage.

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 BiVO4were identified. An orthorhombic form is identical with pucherite and shows a0 = 5.336 Å, b0 = 5.053 Å, c0 = 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 a0 = 5.205 Å, b0 = 11.718 Å, c0 = 5.098 Å, β = 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).

Karibibite, a new FeAs mineral from South West Africa

Abstract Karibibite (ideally, Fe 2 As 4 O 9 ) occurs in vugs in massive loellingite of the Karibib pegmatite area, South West Africa. It is brownish yellow and finely fibrous. The thickness of the soft, single fibers is less than 1 micron, unsuitable for single-crystal X-ray study. Electron diffraction and X-ray powder pattern indicate that the mineral is orthorhombic, with a 0 = 27.91 A , b 0 = 6.53 A and c 0 ( fiber axis ) = 7.20 A . The space group cannot be given. The mineral is paramagnetic with yellow fluorescence and is pleochroic with γ > 2.10, α = 1.96, 2V α large, d = 4.07. It is soluble in acids and alkali hydroxide. Decomposition starts around 320 °C. The infra-red absorption spectrum indicates absence of AsO 4 groups. The mineral is classified tentatively as an oxide or arsenite.