How can one verify the purity of the dust used for Tayammum, especially when collected from the street or from the house after sweeping it, and what are the other conditions for dust suitable for Tayammum?

Tayammum (definition) is permissible only when water is unavailable or when one is unable to use it. The soil used for tayammum must be pure (not ritually impure and not previously used for tayammum), permissible (not usurped or stolen), not burnt, and it must have dust that adheres to the hand.