While sand is a known abrasive (ie, sandblasting & sand paper) it's a pretty interesting subject by itself. What is sand and what does it consist of? There's "rough" and "smooth" sand, even "singing or "booming" sand. Check out these cool sand sites and learn a little more about that pesky stuff we track into the house and go crazy trying to get rid of.
Here in the Seattle area, most of our yards are either based on clay (compressed fine silt) or sand from being on the bottom of Puget Sound. Mine's the sand variety with about three or four inches of pine needles so when it's wet out we get a double decker treat. Today I received the lovely indoor and outdoor mats I ordered from Consolidated Plastics. I liked the oriental look ones, but wasn't prepared to pony up the price and got the basic ones. Even for wall to wall carpet most wear happens in the first ten feet of an exterior entrance and proper walk off mats are important to protect your home's interior. Mats can be brought in to the shop, pressure cleaned and be ready to go home in about a three day turn around time. Cleaning is inexpensive compared to having to fix damage later. If you decide on mats get two sets so you can have one on the floor and one in reserve. We can do your car and truck mats as well!
On a wet, dark, dreary evening check out Tea and Carpets for a real treat. More than just rugs, it's like a visit to a literary salon. Always interesting and a fun read.