This is certainly a useful tool and dates way back to the stone ages. Named Sil Batta in Hindi, it is a flat stone which is used to make Indian chutney and is a very useful kitchen tool. In other countries it is named “batan” and is used to process different kinds of foods in South Asian, South American and Andean cuisine.
In India the “Sil-Batta” and the sil refers to flat stone and Batta referring to the grinding stone. These grinding stones are primarily used to prepare chutney and spice mixes for cooking and occasional use including grinding soaked lentils in preparation for dosa and papadum.
The stone is held in both hands and passed over garlic or whatever you intend to pulverize. Depending on the grind, the stone’s weight is slightly held back, or let loose over and or pressed on.