Olivine is a very interesting mineral indeed. It's stable at higher temperatures than other cheap minerals, leading to olivine sand being used for foundry applications that require resistance to temperatures that would melt quartz. (This is the "refractory sand production" mentioned in the article.) But it's not stable at room temperature in contact with the atmosphere; it has such a strong affinity for CO₂ that it chemically weathers into serpentine, which is mentioned as an alternative later in the article: https://en.wikipedia.org/wiki/Serpentinization

This has led to proposals to grind up olivine into sand and spread it on beaches to reverse global warming, which would definitely work but seems like it could easily overshoot and kick off a new Snowball Earth event.

And, since it composes most of the volume of the Earth, it's a potential source for enormously more iron and magnesium than we could ever hope to mine from mere crustal mines. Drilling rock out of the mantle poses significant technical challenges, though.

The magnesium hydroxide in the second photo is probably more familiar as "milk of magnesia", but, aside from its use as a source of metallic magnesium, it's used in its own right as a refractory insulator in swaged electrical heating elements and basic (high-pH) foundry applications.

I was unaware that it typically had enough nickel and cobalt contamination to be an economically viable source of those minerals.