Dor_42
·So I understand the stated rationale why NASA preferred the hesalite to sapphire but the intended successor, the original Mark II, has a mineral glass crystal. I would think it would behave more like sapphire than hesalite.
As I mentioned earlier in this post, you can be pretty sure that if the Moon landing would have happened today, if there was a Speedmaster on board, it would have had a sapphire crystal. (See latest SpaceX mission, X-33)