eli5: Why does sand which is a bunch of tiny rocks, turn into glass, but we can’t turn big rocks into glass?

Question

I’m very tired. Please help me understand this.

In: Other

Answer 1

Most rocks are a mixture of aluminum and silicon oxides. Silicon oxide melts easily (which is why it makes good glass) but also breaks easily. Aluminum oxide is stronger but is more difficult to work with.

When rocks break down from wind and water, the soft silicon rich pieces get broken more easily into smaller pieces. The smaller lighter pieces get carried by wind and rivers while the bigger and heavier aluminum oxide rich pieces stay. The sand that is good for making glass is the sand that has been carried a long way from the mountain, and has a lot more silicon oxide grains.

So, back to your question. Before rocks can make good glass they need to be ground up and the hard/heavy parts taken out. Nature does this with wind and water.