Zigrasite

Zigrasite can be identified by its hardness of 3 on the Mohs scale, Pale-yellow or light tan color. Look for these key characteristics when examining specimens.

Zigrasite typically appears in Pale-yellow or light tan, also orange to off-white. Color can vary depending on impurities and formation conditions.

Zigrasite has a hardness of 3 on the Mohs scale. This makes it a soft mineral that can be scratched easily.

Zigrasite is an offwhite to pale yellow or light tan in color. Zigrasite exhibits a vitreous luster, and a white streak. The Mohs hardness is 3.The measured( Berman Balance) and calculated densities are 2.76(4) and 2.66 g/cm3 respectively. Zigrasite exhibits imperfect cleavage in two directions, parallel to (010) and (001), it shows no parting, is brittle and has hackly fracture. In transmitted light zigrasite is colorless and non-pleochroic, biaxial negative with indices of refraction α 1.597(1) β 1.622 (1), γ 1.635 (1). Zigrasite is translucent and shows a light blue to pale yellow cathodoluminescence.

Zigrasite is found in association with tourmaline, microcline, quartz, albite, beryl, amblygonite-montebrasite, childrenite-eosphorite, and apatite. It is crystallized as one of the last minerals during pocket formation. The crystals themselves were found perched on a crystal of tourmaline from the giant 1972 pocket at the Dunton Quarry. The quarry itself is located in a complex rare-element granitic pegmatite that has produced large quantities of gem tourmaline as well as many other rare phosphate species.

Zigrasite's atomic coordination consists of two phosphorus sites which are solely occupied by phosphorus and tetrahedrally coordinated by four oxygen anions with distances of 1.532 and 1.533 Å. There are also two magnesium, both of which are occupied solely by Mg and are octahedrally coordinated by two oxygen anions and four (H2O) groups with distances of 2.064 and 2.075 Å. There is a single zircon site solely occupied by zircon and octahedrally coorinated by six oxygen anions with a distance of 2.065 Å. The zircon octahedron shares corners with six (PO4) tetrehedra to form a pinwheel cluster. This cluster forms a fragment of a Zr(PO4)2 sheet which is parallel to the (001) direction. Alternating tetrahedra point up and down relative to the plane of the sheet. Isolated Mg(H2O)6) octahedrea are arranged in layers parallel to (001). These layers are intercalated between the [Zr(PO4)2] sheets linking through the apical vertices of the (PO4) tetrahedra. This structure is formally a heteropolyhedral framework with linkage weaker in the c direction accounting for cleavage.