I wanted half of the necklace to have each stone so when it was doubled as a necklace, it would look like two separate necklaces.
In order to make a necklace like this - the first step is to string all of your gemstones in the order and amount you need to crochet them. The only room for error is on the last set of gemstones - where if you have too many, you can stop the necklace before then and remove them. Otherwise, you have to know how many gemstones are needed for the necklace and how many stitches to make between each stone.
This necklace took some planning and measuring in advance. I strung some of each stone, stitched and measured several times before I had it right.