Aluminium is widely distributed throughout the world in the form of aluminosilicates. What property of these minerals prevents them from being a source of aluminium?

A mineral is any naturally occurring inorganic solid with a crystalline structure and a specific chemical composition (which can only vary within set limitations).

The most abundant metal in the Earth's crust is aluminium. It occurs naturally in aluminosilicate minerals (such as clays and feldspars) and oxides (such as bauxite). However, the Bayer’s process is used to manufacture nearly $90\%$of from mined bauxite.

The bauxite is first cooked in a basic solution to dissolve the oxides ${\mathrm{SiO}}_2$and ${\mathrm{Al}}_2{\mathrm{O}}_3$. The filtrate from the combination is then acidified to precipitate the $\mathrm{Al}(\mathrm{OH}{)}_3$. Finally, the addition of ${\mathrm{CO}}_2$results in the formation of the complex ${\mathrm{Al}}^{3+}$ion, which is cooled and filtered out. When the complexed is dried at high temperatures, the final product is obtained.

Bauxite has a chemical structure that is comparable to aluminosilicates. Thus, a similar approach might hypothetically be used to extract aluminium from aluminosilicates. However, because bf bauxites have a lower boiling point, production from bauxite is cheaper and more cost-effective because $1$mol of $\mathrm{Al}$requires less energy.

Therefore, producing aluminium from bauxite is cheaper and efficient.