It occurs with cerussite, anglesite, smithsonite, hemimorphite, vanadinite, pyromorphite, mimetite, descloizite, plattnerite and various iron and manganese oxides.
[8] Wulfenite crystallizes in the tetragonal system and possesses nearly equal axial ratios; as a result, it is considered to be crystallographically similar to scheelite (CaWO4).
[11] It is argued that no miscibility gap exists in the wulfenite-stolzite solid solution at room temperature due to the almost identical size and shape of the MoO42− and WO42− ions, however, arguments have been made for the existence of a miscibility gap at higher temperatures.
[12] The heat capacity, entropy and enthalpy of wulfenite were determined taking into consideration the existence of solid solutions and the inclusion of impurities.
[12] Molybdenum can be extracted from wulfenite by crushing the ore to 60–80 mesh, mixing the ore with NaNO3 or NaOH, heating the mixture to about 700 °C (decomposing), leaching with water, filtering, collecting the insoluble residues which may include Fe, Al, Zn, Cu, Mn, Pb, Au and Ag, then the NaMoO4 solution is agitated with a solution of MgCl2, filtered, CaCl2 or FeCl2 or any other chlorides is added to the Mo solution and heated and agitated, filtered and the desired product is collected.
Later at 400 °C, a medium endothermic peak represents the second step of the dissociation into lead oxide.
First, the dehydration of hydrocerussite is marked by its loss of constitutional OH and later is the freeing of carbon dioxide during the cerussite dissociation.
The endothermic peaks at 880 and 995 °C perhaps denote the vaporization and melting of unreacted lead and molybdenum oxides.
This reaction occurs as follows: 350 °C: 2PbCO3 → PbO*PbCO3+CO2 400 °C: PbO*PbCO3 → 2PbO+CO2 500–520 °C: MoO 3+PbO → PbMoO4 (wulfenite) Synthesis from molybdite and lead oxide: Thermal analysis for molybdite and lead oxide mixes at a 1:1 ratio suggest that the formation of wulfenite occurs at 500 °C, as can be seen by an exothermic peak at this temperature.
The X-ray diffraction data, calculated cell dimensions, constants and optic axial angles of the synthetic wulfenite are consistent with those of the natural mineral.
[15] Pure wulfenite is colorless, but most all samples display colors ranging from a creamy yellow to a sharp, intense red.
Tyagi et al. (2010) found that a reason for coloration in wulfenite is extrinsic impurity, as they were able to grow crystals displaying red, green, and various shades of yellow simply through changing the purity of the starting charges.
Tyagi et al. note, however, the Mo is in a lower valence state when in Ar ambient, meaning it is Mo5+ rather than Mo6+.
[17] Talla et al. (2013) posits that trace amounts of chromium do in fact play a role in determining the coloration of wulfenite.
They found that as little as 0.002 atoms per formula unit (apfu) of Cr6+ substituting for Mo6+ is adequate to result in an orange-hued specimen.