I believe silica is a cleaner that a bit abrasive depending on the amount.
Silicone is an oil that looks great after you wax.
Silicone oil produces the shine.
The oil attracrs dust.
One rain or wash and the silicone gone along with most of the shine.
The protection from the other ingredients remain for awhile depending on what you use.
Seems Meguiars uses silicone in many if not all their products along with many other companies.
Here's the %'s
Products that contain this ingredient
Brand Category Form Percent
The Right Stuff Gasket Maker-03/01/2001 Auto products aerosol 5-20
Trak Auto Tire Dressing Auto products liquid 10-30
Meguiars Deep Crystal Deep Gloss Polish Auto products liquid 1-5
Rain X Ultra Wax Liquid-09/06/2002 Auto products liquid STP Son of a Gun! Tire Glaze Auto products liquid 10-30
Meguiars Yellow Wax Auto products liquid 1-5
Gunk Silicone Spray Lubricant-11/01/2001 Auto products aerosol
Armor All Tire Foam Protectant-9/07/2000 Auto products aerosol 10-20
Dielectric Grease Auto products grease 75-85
Silicone Adhesive Sealant Clear Auto products aerosol 85-90
Simoniz Advanced Total Car Finish/Polish Auto products liquid
Armor All Flash Black Tire Care Auto products liquid 10-30
Black Magic Professional Protectant Auto products liquid
Armor All Low Gloss Protectant Auto products liquid 10-20
Meguiars Vinyl/Rubber Cleaner/Conditioner-10/01/2003 Auto products liquid 15-25
Westleys Concentrated Paste Auto Polish Auto products paste
Westleys Concentrate Paste Auto Polish Auto products liquid
Liquid Glass Ultra Auto Polish/Cleaner/Finish Auto products liquid 12
Snap Silicone Spray Auto products aerosol 1-5
Trak Protectant Auto products liquid 10-30
Black Magic Professional Protectant-10/31/2002 Auto products liquid 10-50
STP Son of a Gun Vinyl Protectant Auto products liquid 15-30
Meguiars Vinyl/Rubber Cleaner/Condition Auto products liquid 15-25
STP Son of A Gun! 1 Step Tire Protectant-03/12/1998 Auto products aerosol 20-25
Meguiars Deep Crystal Carnauba Wax Auto products liquid 1-5
Rain X The Invisible Windshield Wiper Auto products liquid Armor All Original Protectant Auto products liquid 15-25
The Right Stuff Gasket Maker Auto products aerosol 5-20
Armor All Car Wax 2 Qts. Auto products liquid 1-5
Armor All Protectant Wipes Auto products sheets 10-20
Armor All Ultra Shine Protectant Auto products liquid 25-35
Meguiars Cleaner Wax-05/19/2003 Auto products liquid 1-5
AutoFom Fomblin A Auto products liquid
Simoniz Super Blue Liquid Car Wax Auto products liquid 1-5
Armor All Car Wax, Paste Auto products paste STP Son of A Gun! 1 Step Tire Protectant-07/23/1999 Auto products aerosol 20-25
Classic Aerosol Wax Auto products aerosol 1-5
Westleys Concentrated Liquid Auto Polish Auto products liquid
Liquid Glass PreCleaner Auto products liquid 5
http://www.householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=chem&id=175