Board Thread:News and Announcements/@comment-67.140.221.67-20160930231239/@comment-25396609-20161003032824

Sand is... complicated. It can be created by either wind or water erosion, be intentionally ground down, and so on the composition varied wildly, and only silica sand (effectively finely ground quartz) will make glass, other sands (like calcium and iron) will not, for obvious reasons.

In addition, not all rock has a high enough silica content to become lava which will produce obsidian,

I will admit I was vastly oversimplifying things when i said lava which will make obsidian is composed of molten sand.