Tx, I have a confession: I am fairly sure that I made at least one elementary error in my calculation. I forgot to allow for the density of solid NaCl, which is a bit over 2. The crystal at its most compact would be only about 50 km high, even smaller and harder to find than I had expected.

Mind you, It still would be too steep to survive its own stresses for long. A 40 degree cone, such as you suggested, though not so high, would last longer. 

Also, what is worse, the feng sui benefits would be difficult to achieve, and if achieved, would be temporary. NaCl flows under pressures far more modest than those ambient beneath a 50 km column. The only lamp that might last would have to be incompressible. Hmmm... maybe a few tonnes of a cocktail of alpha- and beta-emitting isotopes in suitably fluorescent ceramics would keep it illuminated for a few million years. I wonder how usefully NaCl itself would glow...