Aventurine is a member of the quartz family with a cryptocrystalline structure. It is usually found in green, red or blue forms and should glitter or show tiny sparkling particles within: green contains fuschite; red, hematite; blue, copper silicates. Stones without sparkle should in strictness not be called aventurines, but rather jaspers.
Regardless of this all aventurines have a special energy that resonates with the Earth very strongly. I find that all aventurines connect me with Archangel Sandalphon very clearly, but most especially the green variety. This is also one of the best crystals for using at the heart centre, or anywhere that balance and gentle healing is required. It also helps connect with the plant Kingdom and her Devic Beings (and with earth and the gnomes). The other coloured aventurines will have resonances specific to their colour thus red will also be energising and grounding useful at base and Earth Star centres (and with fire and the salamanders); blue will also be cooling and calming useful at throat and communication centres (and with water and the sylphs); white will also be clarifying and clearing and useful at any centre, but especially the crown (and with water and the undines).