This is Siva and Uma (Parvati). This form of Parvati sitting on Siva’s lap and embracing him is called Umamaheshwara. For a detailed discussion on Umamaheshwara please refer to this blog.
For a piece of this size, 6.3 cm in height, the detailing is just fantastic. In the front see the work on the crown, third eye, Siva’s belt, the pattern on Siva’s dhoti (lower garment), lines on Siva’s right palm, the lines on Parvati’s saree (lower garment) and the work of lotus petals.In the back notice the necklace, top portion of his Dhoti and his armbands.
The facial features are sharp. It appears this was a part of larger group, see the base/pedestal. No idea as to what it could be.
This is probably from Tamil Nadu, South India, based on the metal, sharp features and the quality of work. There are some wear and tear, more noticeable at the back. I would guess this is from the 19th century and maybe bit earlier.
This site has two other Umamaheshwara and below is the picture of all of them together. What is on this blog is the smallest of the three and it is about 6.3 cm in height.