BK7 vs Quartz vs whatever is better still?

[Jessun]

My Orion (GSO with a sticker) RC has a main mirror made of BK7 glass, and I have now seen versions of this with a Quartz mirror.

Would an 'upgrade' be of any real benefit? Did anyone have an opportunity to compare mirrors of different quality in a similar scope?

[Peter Drew]

As far as I know, BK7 is just a good quality glass with no exceptional thermal properties. Quartz on the other hand has a very low thermal coefficient of expansion and would give its best performace sooner than BK7. Whether this would justify the difference in price is another matter.

[E621Keith]

I think those quartz mirror are probably quartz coated mirror. Growing a quartz crystal into the size of a primary mirror will be very expensive.