An accounting of the dwarves, as explained by half elven scholar Vrenirin Gant.
I apologize for the dry tone of this lecture, and pity the scribe endeavoring to write this.
First off, when we speak of dwarves, we are really speaking of two subraces, the surface dwarves and the deep dwarves. The surface dwarves are accustomed to life in the sunshine, and are the emissaries of their dark delving brethren. The dwarves that humanity and elvenkind interacts with are almost entirely surface dwarves. This interaction has created a misconception that the dwarves look and behaves like surface dwarf culture.
Deep dwarves shun the surface, spending their entire lifetime below the mountain peaks in the dark recesses of the earth. Deep dwarves as you have already surmised, despise the sun. They commonly refer to their surface kin as 'capstones.' Though they try to supress it, deep dwarves have the belief that their surface kin are the weaker of the two subraces. This brings us to the rite of passage known as 'Gharas-akhdrat,' loosely translated this means 'Echoes of the Earth.'
Once a deep dwarf reaches the age of maturity, (40 years of age) they are sent on a series of tests in the deeps to see how well they can mine, craft and fight. This is Gharas-akhdrat. The candidates are divided into groups of five or six dwarves and are accompanied by a judge and mentor (called Dranhds). Sometimes the group can have 2 Dranhds accompanying the group. Gharas-akhdrat lasts up to a month, but can be cut short if the Dranhds see a candidate has exhibited exceptional abilities during the rite, or in the most of unfortunate of circumstances, death or injury befalls the candidates.
If the Dranhds find the candidates worthy of Gharas-akhdrat, they are accepted into deep dwarf society in an event of celebration. This festival is known as The Crystal Song (or Vah-Andha). The Crystal Song entails a lot of singing, drinking and the occasional fornicating. At the end of the festival, the elders determine what occupation the deep dwarf will have. If the dwarf does not like his chosen occupation, he/she can raise an objection with the elders. The objection is then discussed with the candidate and the elders behind closed doors.
If candidates do not pass Gharas-akhdrat, this means exile into the 'Eadh-Deash' (loosely translated, 'The Empty Halls'). Every deep dwarf city has a zone on the outskirts set aside as Eadh-Deash. In addition to those candidates who have failed Gharas-akhdrat, any dissidents or deep dwarves who are deemed 'unhappy' in society are moved (sometimes forcibly) to Eadh-Deash. There have been records of Eadh-Deash housing some 3,000 dwarves.
The deep dwarves only interaction with any residents of an Eadh-Deash is when they arrive to bring more exiles to the zone. Some Eadh-Deash have been known to be periodically wiped out, either by predators, hostile denizens of Rootstone*, disease, or geologic upheavels.
However, about 1,000 years ago, some Eadh-Deash communities banded together and through courage and persistence eventually mined their way to the surface. The particulars of this trend are not outlined here as I'm trying to be as general as I can. What must be known is that these former deep dwarves of an Eadh-Deash became the surface dwarves.
*Rootstone- the deep dwarf general term for all realms underground