Boulder.

The most well know aspect of a Boulder class dragon is a relationship with rocks and or minerals. If you see rock, metal, crystal, sand or ground in the description of a dragon, it's safe to asume it's of the Boulder class.

Many Boulder class dragons eats rocks. Not only do they gain nutrition from it, they can also spit it out as lava.

A comin aspect of Boulder class dragons is having thick scales too help protect themselves.

Dragons that live underground or are known for there digging abilities are also cominly put in the Boulder class.

If you don't know how to seduce a specific Boulder class dragon, show them how much stamina you have. Exercising for a very long time in front of a Boulder dragon you like will no doubt get them hot a bothered. Specifically weight training.