The answer about glass on the Moon depends on where you are and what else you are doing. Oregon L5 Society’s Research Team has used a concept for our Lunar Development Settlement for National Space Society in the virtual world, Second Life, using the basalts of a lava field with a lava tube cave in it, before the end of Phase 1 with in situ resource facilities for producing 3 things:

1. ) Making Liquid Oxygen from regolith electrolysis, which leaves leaves waste highly enriched in reduced Iron, as well as the native Nickel/Iron bits from meteorites pulled out of the the regolith by magnetic rakes before it is fused.

2.) Making the LOX process waste yield Iron Pentacarbonyl and Nickel Tetracarbonyl through the Mond Process, and distilling them to separate the 2, as well as separating the Nickel/Iron bits and their PGM residue. This produces a waste product highly enriched in alumina and silica.

3.) Alumina and silica is most of what you need for high strength “S Glass” fibers from a glass furnace with a spinneret at the bottom and a coating process to keep the glass fibers isolated from water. Calcium from the lunar regolith can be added to lower melting points for separate glass batches. This can be used later with the high melting point fibers, allowing the sort of glass-in-glass composites that Dr. Goldsworthy demonstrated as early as the late 1970s.

Note is this sort of multiple usage of material collected that will lower capital costs for settlements, which costs, after cheap transportation is available, will be their chief limit.