1) Crystal is a crystal, with a high hardness (Mohs level 7), while the hardness of glass is lower,(Mohs level 5.5), the crystal can mark the glass, and vice versa.
Low-e glass comes in two main types hard coat and soft coat. Hard coat low-e glass is produced by depositing a thin layer of metal oxide onto the glass surface during the manufacturing process. This type of low-e glass is more durable and is typically used in commercial applications.