Shell Jasper isn't actually a Jasper but a fossil-bearing variety of Marble that polishes to a lovely smooth, beautifully tactile texture. It has attractive swirls and patterns in white, black and shades of grey. 

Energetically it has a light, gentle quality that is calming and relaxing. It is very smooth, calming, stable and reassuring. This is a good stone to rest with. 

Since this stone is actually Marble, not Jasper/Quartz, it is much softer (3 on the Mohs scale rather than 6/7) and more easily scratched.