Bana Lingam
Stones are ancient and connote divinity. It is a smooth ellipsoid stone. Banalinga is also called the Svayambhu Linga: (Sanskrit) "Self-existent mark or sign of God", as it is discovered in nature and not carved or crafted by human hands. ... The Narmada Shivling are quite strong and the hardness is a 7 on the Mohs scale.