I am a fabricator.

Rule of thumb is max. 12" unsupported cantilever so theoretically you're ok.

However, I've seen 2 instances in 13 years where a chunk of overhang was broken off; once by a teenager hopping up to sit on the counter and the second when two 24 packs of beer were dropped onto a counter.

so - I always recommend modest corbels (like 6 " horizontal) or buried rodding.

Thanks oldryder. So the bookcase area should be fine, but consider supports for the 12" overhang? I found the lg quartz fabricator guide online, and it says their quartz can go to 14" without support. I'm not opposed to some hidden supports though.