How are minerals formed by biological processes?
News to me is that about 4500 of the 4900 minerals on Earth have been created by life.


After reading the article, this isn't what was said.

What was said is that life increases mineral diversity on a planet, most notably through biproducts reacting with existing minerals (like Oxygen - a biproduct of photosynthesis - reacting with iron to create iron-oxide).

So, life doesn't create new minerals, but it does change the abundance of elements at the surface which can undergo reactions with pre-existing minerals to form other minerals.

Not all of the 4500 "new" minerals on the Earth can be attributed to life. We don't know how many new mineral formations have formed because of life, but the article suggests the theory that increased surface diversity of minerals might be a good indicator of life.