http://en.wikipedia.org/wiki/Silicosis

Silicosis (also known as Grinder's disease) is a form of pneumoconiosis caused by inhalation of crystalline silica dust, and is marked by inflammation and scarring in forms of nodular lesions in the upper lobes of the lungs.
Types of Silicosis

Classification of silicosis is made according to the disease's severity, onset, and rapidity of progression. These include:

Chronic silicosis
A form of the disease that develop after 20 years or longer of exposure to low levels of silica dust. Chronic silicosis itself is further subdivided into simple and complicated silicoses. This is the most common type of silicosis.

Asymptomatic silicosis
Early cases of the disease do not present any symptoms

Acute silicosis
Silicosis that develops after 1 to 3 years of exposure to very high concentration of silica dust.

Accelerated silicosis
Silicosis that develops after an average of 10 years of exposure to high concentration of silica dust.
I'm thinking if you've smoked a bit of this stuff it probably won't hurt you... but if this shit stays around, it could pose some pretty severe health problems with prolonged use.