Why might a dry atmosphere cause your crystal to fracture and to eventually become a
white powder?

Causes when dry atmosphere create crystal to white powder is explained below.

Explanation:

Efflorescence is the loss of water from the chemical structure of a mineral. A small number of hydrous minerals may partially lose the water in their structure if kept in dry or hot areas. This causes the mineral to form a white powder on its surface, and decreases its transparency.

The technical name for this white powder is Efflorescence (from the French, meaning “to flower out”).  It is an accumulation of minerals and salts on masonry surfaces, such as brick, cement, and sometimes stone. Building inspectors and home owners should know how to prevent  and remove this unsightly residue. They must also be aware that, while efflorescence in itself is not a problem, it is a symptom of a problem, namely the presence of excess water in the masonry, which can lead to more serious structural and health issues.

During the summer, it is not unusual for the temperature in these attics to run around 160 – 165 F.  Long story short, I sweat alot because of this.  I wear a cap (below) to keep insulation out of my hair, bit it also acts to absorb the sweat from my forehead and keep it out of my eyes.  This sweat (which is just salt water) is wicked up the cotton fabric of the hat and the water evaporates.  As it does, it leaves the salt behind, creating white stains on the cap.  This is the human form of efflorescence.

As with mold, the appearance of efflorescence varies greatly. It can be powdery, it can have sharp edges and be easy to spot, or it can have indistinct edges. It can cover a large area as a fine dust, or form large individual crystals. Its appearance depends partly on the type of salt from which it is composed, but also on humidity levels (both inside and outside the house), and local rainfall and winter temperatures during the last few years. In exceptionally dry climates, water can evaporate before it even reaches the surface, in which case the salt will accumulate unseen beneath the surface. In humid areas, moisture may take a long time to evaporate, allowing the slow growth of “whispers” projecting from the surface.

answer carbon and three oxygen atoms;