Silica

CAS ID #: 7631-86-9

Affected Organ Systems: Immunological (Immune System), Renal (Urinary System or Kidneys), Respiratory (From the Nose to the Lungs)

Cancer Classification: EPA: Not evaluated. IARC: Carcinogenic to humans . NTP: Known to be a human carcinogen

Please contact NTP, IARC, or EPA’s IRIS Hotline with questions on cancer and cancer classification.

Chemical Classification: Inorganic substances

Summary: Silica is another name for the chemical compound composed of silicon and oxygen with the chemical formula SiO2, or silicon dioxide. There are many forms of silica. All silica forms are identical in chemical composition, but have different atom arrangements. Silica compounds can be divided into two groups, crystalline (or c-silica) and amorphous silica (a-silica or non-crystalline silica). c-Silica compounds have structures with repeating patterns of silicon and oxygen. a-Silica chemical structures are more randomly linked when compared to c-silica. All forms of silica are odorless solids composed of silicon and oxygen atoms. Silica particles become suspended in air and form non-explosive dusts. Silica may combine with other metallic elements and oxides to form silicates.