وَيَجُوزُ التَّيَمُّمُ عِنْدَ أَبِي حَنِيفَةَ وَمُحَمَّدٍ بِكُلِّ مَا كَانَ مِنْ جِنْسِ الْأَرْضِ، كَالتُّرَابِ وَالرَّمْلِ وَالْحَجَرِ وَالْجِصِّ وَالنُّورَةِ وَالْكُحْلِ وَالزَّرْنِيخِ. وَقَالَ أَبُو يُوسُفَ: لَا يَجُوزُ إِلَّا بِالتُّرَابِ وَالرَّمْلِ خَاصَّةً.
Meaning: Abu Hanifa and Muhammad permit tayammum using anything of the earth's genus, such as soil, sand, stone, gypsum, lime, kohl and arsenic mineral. Abu Yusuf permits soil and sand specifically.
The difference concerns what counts as valid earth material, not whether the earth used must be pure.