Which is better? Why is Granite favored over the new engineered stones?
A vug is a natural void in a rock, and yes this is where rock crystals commonly grow. They are very common in limestone (pahasaps/madison formation, for example), forming calcite crystals. They are also common in volcanic areas, and rifted areas, such as thunder bay Canada. Crystals have some value, especially if it's a pretty specimen, but even gigantic ones (4 feet x 1 foot) only go for a thousand dollars or so. Check OKorder for geodes or quartz crystals. Continuing to grow the crystals would probably be possible, but it wouldn't be efficient, easy, or fun. Most likely it will just coat the entire rock in a powdery coat, wrecking it. You would want to start with a hot solution of silicic acid, and find some way to keep it mobile and saturated. The saturated solution and the heat would speed up the process. Vugs like that, especially with quartz occasionally contain gold. Might want to take a close look.