Interesting Pair of Quail Solid and Heavy, Ferrous (Iron w/coating?) Japan

Description

This is a very interesting pair of quail made in Japan. They are ferrous (a magnet will stick to them) and they are covered with a thin coating of something else that can be scratched off. Where a scratch is shallow it is powdery and an orange color, like clay, but below this there is a green powdery layer like oxidized metal. Please zoom in on the pictures to see the condition and small orange and green spots. They could also be made of clay or a soft stone with a high iron content. I am not sure what they are made of. They are heavy for their size.
The larger one is stamped Japan on the bottom. The smaller one is not marked. They are solid and heavy and weigh 1 lb 14 oz together. The larger one is approximately 3-1/2 inches tall, 3-1/2 inches long, and 2-1/2 inches wide. The smaller one is 2-1/4 inches tall, 3 inches long, and 2 inches wide.
Thank you for looking!