Bhakti-rasāmṛta-sindhu .4.263
karkaśaṁ trividhaṁ proktaṁ vajraṁ svarṇaṁ tathā jatu |
[karkasham trividham proktam vajram svarnam tathaa jatu |]
citta-traye ’tra bhāvasya jñeyā vaiśvānaropamā ||263||
[chitta-traye ’tra bhaavasya jneyaa vaishvaanaropamaa ||263||]
Blended reading (Sanskrit + English inline)
karkaśaṁ trividhaṁ proktaṁ vajraṁ svarṇaṁ tathā jatu |
citta-traye ’tra bhāvasya jñeyā vaiśvānaropamā ||263||
There are three degrees of hardness: like a thunderbolt, gold and lac. Bhāva is like fire in relation to these three types of hard heart.
Purport
A hard heart is compared to a lightning bolt, to gold and to lac.
— A.C. Bhaktivedanta Swami Prabhupāda
My note
Source: vedabase.io