Is sponge cake a heterogeneous mixture

though many may argue that cake batter is a homogeneous mixture because of its observable uniformity, we know it is heterogeneous. ... In other words, the mixture of ingredients from cake batter results in some chemical reactions here and there, but we are still left with a mixture of things that can be separated.

Explanation:

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).