Benefits of using lava rock as a soil additive
Lava rock is a mineral that forms when magma from volcanoes solidifies and hardens into rock. It is then crushed to multiple grades for different uses. It's hard-wearing, water-permeable, breathable & durable: it takes a very, very long time to break down.
When used in a soil mix, its porosity allows bacteria & fungi to live in and on it, improving microbial life. In addition, the porosity of it also allows it to absorb and release water assisting with any over or underwatering to a certain extent.
Lava rock tends to stay in place in the soil whereas with other alternatives such as perlite & vermiculite, you may find that over time they work their way up to the surface of your soil.
When looking at the sustainability of lava rock compared to other products, lava rock is also more environmentally friendly: both perlite and vermiculite must be heated to almost 1,000 deg. C to make them, resulting in a great deal of carbon emission, whereas lava rock doesn’t need any processes other than shallow mining it (lava rock is deposited on the surface of the earth when a volcano erupts, so blasting and other destructive mining methods are not necessary).