Caitanya-caritāmṛta 6.279
lohāke yāvat sparśi’ hema nāhi kare tāvat sparśa-maṇi keha cinite nā pāre
[lohaake yaavat sparshi’ hema naahi kare taavat sparsha-mani keha chinite naa paare]
Blended reading (Sanskrit + English inline)
lohāke yāvat sparśi’ hema nāhi kare tāvat sparśa-maṇi keha cinite nā pāre
As long as it does not turn iron into gold by its touch, no one can recognize an unknown stone to be a touchstone.
My note
Source: vedabase.io