Lava Rock or volcanic rock is quite a popular decorative material in yard landscaping. It belongs to the category of igneous rocks and is formed when erupted lava cools down.
It is porous in nature and also has air bubbles that pop as it dries. The air bubbles are the reason why lava rocks are really light and also why they have bubble-shaped holes throughout.
Lava rock is available in three colors; reddish-brown, black, and gray. The minerals present in the rock and the cooling process determine its color. The reddish-brown tint appears only if the iron in the lava begins to oxidize when it is cooling down.