I prefer not to luse loamy type of soils in a terrarium for the simple reason that they tend to clog up over the course of time due to decomposition and make changing the soil base necessary in due time. Rather I opt for bedding types of substrates that are mostly wood products and that can be mixed with other natural products such as twigs and leaves from hardwood trees and various grades of gravels to help extend aeration life. One of the commercial products that I enjoy using is by T-Rex, called
Jungle Bed-click here to see

If the plants you are planning on using in your terraria are finely rooted then you may want to opt for a blend of a fine fir bark, peat moss, and freshwater sand that can be enhanced with ground up hardwood leaves and a fine grade of gravel.

How about lava rock?

Hi Terrestrial... I should have clarified that I want a loamy look, not a loamy soil.

Anyone know where to get lava rock? The prices on repotme.com seem to be pricy.

Thanks!
Jeff

Lava rock is very easy to find at Lowes, HD and other BBSs -- especially in the spring/summer.

LOL oopz typo... *chunks can be purchased from........