Since the other thread is revolving primarily around the Jaslow Arena, I'm taking this idea outside of the thread, even though its still relevant since people are focusing on just that one specific part of Negav. Here's an idea I worked on with Amaroq about the material used for Negav's Building Material - which looks like standstone.
To reiterate, hauling standstone from akaptor desert, the nearest available source is ridiculous and doesn't make sense - neither does importing sandstone from off world - even so connection to those worlds wasn't around back in the old days. This fixes both those problems.
Takrit
Uncommon
Takrit is a sedimentary rock, similar to sandstone (which is also sedimentary), and taking on a similar color as well. It is found semi-commonly underground and used to considered precious until traces of one of the larger deposits in Felarya was discovered right underneath where Negav is located when the ancient tunnels were dug thousands of years ago. However, the sediment also has micro-crystalline materials embedded into it from deep underground - in addition to a cementing material, where it has been subjected to pressure and heat enough to form into a stone much harder than sandstone. Due to the micro-crystalline materials it is also capable of being enchanted, and also transmuted as well.
When subjected to heat magic, the micro-crystalline substructure helps morph it into an even denser rock almost as strong as metamorphic. The refined Takrit is very smooth and a beautiful gold-like color. As such even poor housing districts in Negav look nicer than they would otherwise because of this stone's slightly altered properties.
Takrit is also often used as an aquifer for groundwater, or as a reservoir for oil and natural gas - especially when shipped off to other civilizations from the portal.