Matsya Purana — Division of Bhārata-varṣa
नीलवैडूर्ययुक्ते ऽस्मिन् सिद्धा ब्रह्मर्षयो ऽवसन् दैत्यानां दानवानां च श्वेतः पर्वत उच्यते //
nīlavaiḍūryayukte 'smin siddhā brahmarṣayo 'vasan daityānāṃ dānavānāṃ ca śvetaḥ parvata ucyate //
In this region, adorned with blue vaidūrya gems, Siddhas and Brahmarṣis dwell; and it is said to be the White Mountain associated with the Daityas and Dānavas.
This verse is not about Pralaya; it belongs to sacred geography, describing a gem-adorned region and the beings associated with a mountain called Śveta.
Indirectly, it supports the Purāṇic ideal that rulers and householders should honor tīrthas and sacred regions—places where Siddhas and great sages are said to dwell—by pilgrimage, patronage, and protection of dharmic sites.
No direct Vāstu rule is stated, but the verse reflects a Purāṇic motif: sacred spaces are described as “adorned” (yukta) with auspicious materials (gems), a theme later echoed in temple iconography and sanctum ornamentation ideals.