Lava rock and lava sand are two different creatures, even though they're the same material. Lavasand is a relatively fine material that is mixed into the soil. It helps with micro nutrients for the soil and mostly it helps retain moisture.
Lava rock, like the sand (crush rock), is mined from volcanic areas, mostly in Mexico and mostly in the Pinacate mountains. It is used to cover the ground and people often put it on top of landscape cloth. The plastic "cloth" is not a good choice.
You can get lavasand at nurseries and feed stores. I don't know if you can get it at the big box stores. I'm sure you probably can get bags of the rock in more places.
_________________ Northwesterner
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