1) Granulated and ground spices are legal. However, "powders" are illegal, including onion powder and garlic powder. So for example, "ground black pepper" is legal, but garlic powder is not legal.
2) Silicon Dioxide: As a supplement/pharmeceutical ingredient it is used in tiny amounts. Anti-caking ingredients in foods can be problematic.
For example cellulose in supplements is okay; but large amounts of (processed) cellulose in foods (for example: cellulose added as an anticaking agent in pregrated cheese) is too hard to digest for SCDers.