A diamond cloud comprises a bunch of pinpoint inclusions numbering three or higher. Pinpoint inclusions look like dots under 10x magnification, and some are too small to even show up. As a group though, they look like a gray or white patch.
Effect on Clarity
Clouds, based on their density and size, can cause murkiness that leaves the stone devoid of the fire, which is the most characteristic thing about a diamond. If the cloud covers more than one-third of the stone, the latter can look almost ugly.
Effect on Durability
Pinpoints – and Clouds, by extension – do not overlap with the crystal structure, which means a stone containing these is not rendered any more vulnerable to damage. Internal diamond clouds may even go unnoticed for a long while, which is why it is important to check any diamond closely before buying it.