# Question #2ca99

Mar 3, 2017

The glass slowly crystallizes as it ages.

#### Explanation:

Most glass is an amorphous form of silicon dioxide, ${\text{SiO}}_{2}$.

In contrast, the atoms in quartz, the crystalline form of ${\text{SiO}}_{2}$, are in a highly ordered arrangement.

(From Reddit)

As time passes, the glass is subjected to many temperature changes, such as from day to night.

Over a long period, small areas within the glass will crystallize.

These crystalline areas scatter the light in different directions, causing the glass to appear milky.