Two separate conditions govern valid material: it must belong to an acceptable earth-based class under the relevant juristic opinion, and it must be pure.
A stone may qualify as earth material, but a known impurity on it still prevents treating that surface as pure earth for tayammum.
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Tayammum Materials, Intention, Nullifiers, and Searching for Water
Two separate conditions govern valid material: it must belong to an acceptable earth-based class under the relevant juristic opinion, and it must be pure.
A stone may qualify as earth material, but a known impurity on it still prevents treating that surface as pure earth for tayammum.