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.

The ions of magnesium, nickel and cobalt have almost the same size (iron ions are slightly larger, and manganese ions even larger).

That is why nickel and cobalt may easily substitute magnesium in magnesium minerals, being more enriched there in comparison with nearby minerals containing iron oxides or manganese oxides.

However, even the bigger ions of iron and manganese do not differ much in size of the magnesium ions, which is why in olivine some part of the magnesium ions are substituted with iron or manganese ions, besides the nickel and cobalt ions, because iron and manganese are very abundant everywhere, even if they do not fit as well the crystal structure as nickel and cobalt.

The serpentinization process is an alternate history humanity saver. Here's a crazy long article that has an analysis smack dab in the middle of it: https://worksinprogress.co/issue/olivine-weathering/ .

I seem to remember that one off the Central American countries has actually built a "green beach"; but, for the life of me, I can't find it. I may just be misremembering.