I read this Sanskrit shloka in a book.

>पृथिव्यां त्रीणि रत्नानि जलमन्नं सुभाषितम्। मूढ़ै: पाषाणखण्डेषु रत्नसंज्ञा विधीयते।। 
> 
> Prithivyaam trini ratnaani jalamannam subhaashitam | Mudeih paashaan-khandeshu
> ratnam-sagyaa vidhiyate ||

Is it mentioned in any Hindu scripture? From where is it taken?