Garudapurana 1.70.25

1.70.25

saṃprāpya cotkṣipya yathānuvṛttiṃ vibhartiyaḥ sarvaguṇānatīva /
tulyapramāṇasya ca tulyajāteryo vā gurutvena bhavettu tulyaḥ /
prāpyāpi ratnākarajā svajātiṃ lakṣedgurutvena guṇena vidvān //

and that which, having been taken and weighed according to custom, exceedingly possesses all virtues, / or which is equal in heaviness to one of equal size and equal class— / even when found in the ocean, a wise man should identify its true class by weight and quality.