What is isomorphous salts..?

The salts having the similar crystal strucure are called isomorphous salts

In crystallography crystals are described as isomorphous if they are closely similar in shape.^[1] Historically crystal shape was defined by measuring the angles between crystal faces with a goniometer. In modern usage isomorphous crystals belong to the same space group.

Double sulfates, such as Tutton''s salt, with the generic formula M^I₂M^II(SO₄)₂.6H₂O, where M^I is an alkali metal and M^II is a divalent ion of Mg, Mn, Fe, Co, Ni, Cu or Zn form a series of isomorphous compounds which were important in the nineteenth century in establishing the correct atomic weights of the transition elements. Alums, such as KAl(SO₄)₂.12H₂O, are another series of isomorphous compounds, though there are three series of alums with similar external structures, but slightly different internal structures. Many spinels are also isomorphous