Terracotta Tokens From The Persian Gulf?

Hello everyone:

Several years ago, I bought the following pieces, described as "terracotta tokens from the Persian Gulf," from a well-known dealer of world coins on the internet.

They range from 9mm to 12mm in diameter and between 1.5mm to 2mm thick. The dealer said they're from the 11th and 12th centuries, when merchants minted them to provide small change. Other than that brief description, I haven't been able to find anything about them.

Does anyone know where I might find more information about these? Is there any reference (book, article) that discusses them and the circumstances under which they were created in greater depth?

Many thanks in advance.