This is one thing that I've never been able to find a pattern for so I managed to come up with a version which works :)
This pattern is worked in continuous rounds to create the spiral shape of the shell, do not join with a sl st at any point.
I apologize in advance if the pattern is difficult to understand as I am unsure of how to write a pattern for something that doesn't have rows or rounds XD
You can use any size hook and any kind of wool for this project
Begin with a magic loop
5 sc in the magic loop
Tightly close the loop
Sc into the top of the 1st sc
2 sc into each of the next 7 sc
2 hdc in each of the next 7 sc
2 dc in each of the next 4 sc
3 tr in each of the next 2 sc
Finish off and weave in ends
To add a different coloured edge to the shell, pick a different colour,
Put your hook through the hole of the magic loop and draw up a loop,
Begin slip stitching through your design, following the spiral,
When you reach the end of the interior spiral and come out at the side when the edge is, just begin to single crochet in each sc to the end,
Finish off and weave in ends.
You can use whatever colors you like for this to create some interesting effects, these are some that I did with some odd bits of wool I had laying about.
As always, please feel free to comment and share the color combinations you used :)