> The basalt fibers typically have a filament diameter of between 10 and 20 μm which is far enough above the respiratory limit of 5 μm to make basalt fiber a suitable replacement for asbestos.
The source mentioned is a basalt fiber brand website, so not sure if that's enough for confidence.
And they aren't wrong, inhaling basalt fibers is dangerous and long term exposure could injure or kill you. It's just a different mechanism than asbestos. https://en.wikipedia.org/wiki/Silicosis
See for example this MSDS for basalt. https://mcdn.martinmarietta.com/assets/safety-data-sheets/ba...
> The major concern is silicosis (lung disease), caused by the inhalation and retention of respirable crystalline silica dust.
(NB: I do not know if or claim that basalt fibers are more dangerous than alternatives.)
For what it's worth, the ex-composite-shop guys I used to work with said that basically everything you can make a composite out of is horribly nasty: carbon fiber, fiberglass, basalt fiber, probably anything period. After repeated exposure you develop contact dermatitis to that type of fiber and the shop moves you on to working with something else, until it happens again. Contact dermatitis is just the first visible sign, it gets worse from there. Eventually you're probably going to want to get out of the shop entirely.