While more work was being done on Pokémon Lapis & Carnelian, I figured that I should introduce a new type that was recently added into the game; the Glass-Type.
To give a more detailed description as to how this all works, you might have also noticed that the Normal-Type actually has an advantage over something for once. This is a reference to how flimsy, and easy to break glass can sometimes be in situations that don't benefit the substance. This is also due to the fact that the Normal-Type has no advantage over any existing type in the canonical Pokémon games, and some people even suggested that the Normal-Type should be super-effective against itself which, if you ask me, that sounds like a pretty broken type. I did plan for the Normal-Type to be resistant against the Glass-Type, but dropped this idea, because we decided to keep it a basic type.
Everything else is based purely on the density of glass and how it's made. Glass is immune to Ground, resistant to Poison, in addition to being super-effective against both types, because chemicals and sand are often used to create glass. In fact, if the Nuclear-Type from Pokémon Uranium were to be added to Pokemon Lapis & Carnelian, the Glass-Type would be super-effective against that type too. Everything else is just common sense match-ups, Glass is sharp enough to cut Grass, while bugs, birds, and other flying animals are hurt by it because it appears invisible from a certain distance, causing them to collide with it.
While debating on what to do with the Fire-Type, the decision was made to make the Glass-Type resistant, as intense heat is of fundamental importance in the creation of Glass.
Most of the attacks in-game are based on glass blowing, polishing, and breaking, and there's even an Ability unique to this type called Crystallize, which turns Normal-Type attacks into Glass-Type attacks in addition to boosting them slightly.
Currently, the first Pokémon being designed to fall under this type is a regional variant of Chandelure with its default Ability, Flash Fire replaced by another Ability currently unique to Glass-Types.
Fun fact: While Pokémon Lapis and Carnelian was still under the concept phase, the Crystal-Type was added as an early prototype to the Glass-Type.