Seen the 100 gems many times and have gotten them once. It was on the 5th lab for the day. I run 3 per day unless I get gems as a reward. If I get 10 I run the 4th and if I get enough to cover the 5th I run it. Saturday past I got 80 gems in rewards. Don't know if its just me but seems like the faster I run them the better the rewards. Here is the kicker though, even though they are randomly generated they still pattern themselves. It's tedious at first but map out the top 4 or 5 rows (or the whole path you take) as you play and after several dozen you will see a hint as to which way to go. It's still luck of the draw what the spaces are but even some of them are predictable. And I know.... way too much time on my hands but it was a long cold winter.