Shell Jasper is also known as Shell Marble, Sea Shell Jasper and in China as “Thousand Eye Stone”. Although Shell Jasper is marketed as jasper, it is actually marble, a metamorphic limestone, with a compact and crystalline texture that can be polished to a high gloss. It contains fossils of Gastropods and Bivalves that have somewhat metamorphosized but still appear in their distinctive shapes.
See photo for scale. They are on average around 6-7mm thickness.