The chemistries of the Tungstate ion (WO4) 2-, and the Molybdate ion (MoO4) 2-, are so similar that the groups of minerals are always associated, with extensive solid solution between the two extremes. The anions are distorted tetrahedra with the central Tungsten or Molybdenum atom bonded to four oxygen atoms by largely covalent bonds. The overall charge of the Molybdate or Tungstate ions is -2 which is usually balanced by divalent metals such as Iron, Calcium or Lead. Tungstates are very important industrial minerals yielding Tungsten metal, which when alloyed with iron, produces a strong corrosion-resistant steel. The metal is also extensively used in the manufacture of filaments for light-bulbs and vacuum tubes.

The basic structural element of Chromates is the Chromate ion (CrO4)2-. The tetrahedral arrangement is identical to tungstate and molybdate ions. The net negative charge is balanced by divalent metal ions, such as lead, packed amongst the tetrahedra and holding the structure together. The size of these metal ions and their interstitial packing detemine the overall structure. Chromates are an important source of metallic Chromium which is often used for electroplating steel to prevent its corrosion. Chromite, FeCr2O4 is the major ore. There are 15 recognised Chromate minerals which fall into one of four solid solution series; Tarapacaite - Crocoite, Wattersite - Satanaite, Embreyite - Cassedanneite and Lopezite.

The Tungstate-Molybdate minerals are divided into the following groups:

Wolframite Group - is a solid solution series between Ferberite (FeWO4) and Huebnerite (MnWO4). Both the manganese and iron are in the 2+ oxidation state. Pure members are very rare and most specimens consist of a mixture of these two minerals. The name Wolframite (or Tungstite) is applied collectively to these intermediate minerals. They are very important ores of metallic tungsten.

Scheelite Group - is an incomplete series between Scheelite (CaWO4) and Powellite (CaMoO4). The minerals toward the Scheelite end (Ca(WO4,MoO4)) are commoner and usually referred to collectively as Scheelite. Some are highly fluorescent. The group's structure features the (WO4)2- and (MoO4)2- ions as flattened tetrahedra with Calcium ions in between holding the crystal structure together.

Wulfenite Group - in contrast to Scheelite and Wolframite these are secondary minerals formed by the alteration of primary Lead ores in the presence of Molybdenum or Tungsten. The stucture is the same as the Scheelite group. Wulfenite is the name given to specimens in a solid solution series between Wulfenite (Pb(MoO4)) and Stolzite (Pb(WO4)), although a complete solution has not been found in naturally occurring specimens. Many specimens have a degree of Ca2+ substitution in place of the Lead.