The rectangular shell is approximately 4 cm (1 1/2 inches) long, & 2.5 cm (1 inch) wide. Each shell is a bit different but the size & shape are the same; you will receive one very similar to the photos.
Despite its size, the pendant is very lightweight. It can be slipped off the 40 cm (16 inch) sterling silver chain if you wish, & added to your own necklace or chain.
I currently have this style of shell necklace in stock in purple as well: https://www.etsy.com/listing/158926240/pink-abalone-necklace-rainbow-shell
A lot more abalone here, in many colours: http://etsy.me/13ScKbL