This Linga is the aniconic form of Shiva. What makes this Vigraha unusual are the face (single face and hence Ek Mukh) and the cobra wrapped around the central portion. The facial features help us in identifying its origin, in this case, Nepal.
It is solid cast and quite heavy. There is some rattling sound in the lower portion. May have something to do with the consecration process/material.
It is gilded and looks to have been in worship for a long time. At some stage, before I got it, there must have been an attempt (thankfully weak) to clean it.
It is about 9.5 cm in height.
Several stone sculptures of this kind of Linga exist, mostly from North India. The date from the first century of the Common Era. Examples made of metal are rarer. The Manifestations of Siva by Stella Kramrisch has two examples. The rarity makes estimating the age bit challenging. My best guess is this example may be from the 16th century or earlier.
Note about the spouted part: Quoting Dr Pratapaditya Pal, “Nepa/Where gods are young“, Page 126 Cat item 55. ” The original purpose of the spouted container was to drain off the liquids that were poured over the Linga as part of a ritual bath. Later, however, due to the strong emergence of the Sakti cult, the container came to be regarded as the yoni, the female sex symbol”. Almost all the early representations of Linga have only the central shaft and not the spouted part. Gudimallam lingam is one such example.