According to the Shiv Purana:-

According to the Shiv Purana, any Rudraksha that does not have a naturally formed central hole or is not naturally round or oval in shape should be rejected and not worn. The scripture advises devotees to choose only naturally formed Rudraksha beads, as they are regarded as the proper and auspicious form for spiritual use. Selecting authentic, naturally occurring Rudraksha is considered essential for preserving its traditional sanctity and spiritual significance.

The relevant verse states:-

एकवक्त्रः शिवः साक्षाद् ब्रह्महत्यां व्यपोहति॥
Ekavaktraḥ Śivaḥ sākṣād brahma-hatyāṁ vyapohati.

Translation:-

"The One-Mukhi Rudraksha is the direct manifestation of Lord Shiva. It is traditionally believed to remove even the gravest sin, Brahmahatya."

What a 1 Mukhi Rudraksha Should Be (Based on the Shiv Purana)

The scripture implies only one physical criterion:-

• It should have one natural mukha (one natural longitudinal cleft or face) running from one end of the bead to the other.

• It is regarded as the embodiment of Lord Shiva.

• It is considered the most spiritually significant among Rudrakshas.

What the Shiv Purana Does Not Mention:-

The Shiv Purana does not state that a 1 Mukhi Rudraksha:-

• Must be half-moon or cashew shaped.

• Must come from Nepal, Indonesia, or any other specific region.

• Must have a particular size, color, or surface texture.

• Should be identified by any laboratory or X-ray criteria.

These descriptions originate from later traditional texts, regional practices, or the modern Rudraksha trade, not from the Shiv Purana itself.

A Concise Statement for Educational Use:-

According to the Shiv Purana, a genuine 1 Mukhi Rudraksha is a naturally occurring bead with a single mukha (one natural line or cleft). The scripture identifies it as the direct manifestation of Lord Shiva and emphasizes its spiritual significance rather than its physical appearance, size, shape, or geographical origin.

This wording is faithful to what the Shiv Purana explicitly states and avoids attributing later traditions to the scripture itself.