Vermiculite is a complex hydrated aluminum and magnesium silicate and its average composition, can be represented by the formula 22MgO.5Al₂O₃ 22SiO₂.4H₂O.

When heated it exfoliates many times. Expansion below 10 times is considered as low-grade. It shows characteristic micaneous structure of basal cleavage not as perfect as mica and occurs as soft, pliable and elastic laminae. The property of exploration together with the development of golden bronzy or silvery lustre on heating is the outstanding characteristics or vermiculite.

Vermiculite owes its commercial utility because of the property of exploitation on heating. Its low bulk, comparatively high refractoriness, low thermal conductivity and chemical inertness make vermiculite satisfactory for many types of thermal and acoustic insulation. In India, its use is confined to the manufacture of lightweight bricks for insulation, as a packing material, as filler in plastic and in horticulture. Unexfoliated vermiculite is used in drilling mud, in the annealing of steel etc.

There is no BIS specification for vermiculite. However, vermiculite of the following specifications is generally used for making lightweight bricks.

Physical: - 8 + 16 BSS mesh and exfoliation should be more then 8 times.

Chemical:
SiO2	36 to 37%	Al2O3	14 to 16%
Fe2O3	10 to 14%	TiO2	3 to 4%
CaO	2 to 2.5%	MgO	17 to 19%
L. O. I.	6 to 8%	Moisture	2 to 3%

Its use in soil conditioning is well established.

No end use grade classification of reserves attempted due to lack of data from exploration/exploitation agencies.

The following end-use specifications for estimation of reserves are prevailing.

Thermal Acoustics and insulation:

SiO2	36% (min.)
Al2O3	16% (max.)
MgO	15% (min.)
Exploration	8 times (min.)