Pure dust for Tayammum:
One of the distinctive features of the Ummah of Muhammad  is that the earth has been made a means of attaining purity (Saheeh Muslim 523, Sunan Abi Dawood 489). In other words, if one is not able to use water for the purpose of purification, one is permitted to wipe parts of the body with clean earth or sand. This is called Tayammum.
Conditions for validity of Tayammum:
1. The intention to attain purity or to perform salaah.
2. To search for water if there is hope in obtaining it.
3. Unable to use water.
4. To perform Tayammum on clean sand or anything which falls under the term “earth”.
5. Not leave the space of even a hair unwiped.
6. To utilize at least three fingers during Masah.
The method of Tayammum:
1. Make the intention to attain purity or to perform salaah.
2. Strike the earth while keeping the fingers apart.
3. Once on the ground, move the hands forward and then backward.
4. Shake the dust off the hands.
5. Wipe both hands over the entire face.
6. Strike the hands on the ground and move them forward and backward as before.
7. Wipe the right arm with the left hand, upto and including the elbow.
8. Wipe the left arm with the right hand, upto and including the elbow.