Richard

Vermiculite is used in agriculture for:
(1) an ingredient when making a soil from raw materials, and typically in a fine-grained soil for seed starts or small potted plants.
(2) as a covering on newly planted seeds -- especially when surface-sown in "plug trays".
(3) a soil-less media in hydroponics.

For my clients who have fast-draining sandy soils, we mix in composted vegetative matter (at least 50%) to slow down the drainage and introduce carbon compounds into the soil. In extreme cases, we also add one ground-up brick of coir (1/2 cubic foot) per cubic yard of soil.

To improve clay soils, you need
(1) A source of acid to disassociate the clay minerals, typically ground-up sphagnum peat moss and/or humic acids.
(2) Larger grain sands, such as horticultural sand (in rock quarry jargon, it is 1/8th inch plus, 1/4 inch minus screened crushed cobble).
(3) A "sturdy" porous aggregate, such as 1/4 inch "plus" scoria or hard pumice. As a measure of the latter, if you can crush it with your foot it is not hard enough.
(4) Organic (vegetative) matter, preferably cured fine-grained compost.
(5) A small amount of worm castings or red-wriggler worms if not already present.
(6) A 3- to 4-inch thick layer of composted mulch, typically 1-inch diameter material with some fines and some longer pieces. This will provide a great environment for the worms and other beneficial critters to live in.

First of all, "perlite" and "expanded shale" should be selling for the same price per volume and a retail price of more than $3 per cu.ft. is expensive.

Second, "perlite" and "expanded shale" are different and have different uses. Perlite is a soil aerator for modest size pots and short term plantings -- you wouldn't use it in a soil for a permanently boxed tree. Expanded shale is a medium for florists, hydroponics, cymbidium orchids, some bromeliads, etc.

__________________
Back in business at plantsthatproduce.com