In gemology, the presence of such inclusions is regarded as 'diagnostic' for natural demantoid (i.e. these inclusions are not found in any other green gemstone).[12] Some gemstones are more valuable for their inclusions,[13] and 'horsetails' can be regarded as desirable features in demantoid, as they are taken as an indication of prestigious Russian origin,[10][14] although some demantoids from certain other locations (such as Italy and Iran) may also contain 'horsetails', which are regarded as being characteristic of a serpentinite geographic origin,[15] and, on the other hand, not all Russian demantoids actually contain 'horsetails'.[16] The microstructure of some demantoids is believed to be affected by the presence of 'horsetails' (the 'horsetail' typically originates towards the centre of the nodule, with the fibres branching out and radiating towards the surface), whereas horsetail-free demantoids from other sources frequently display flat crystal faces.[17]