Silica is seen commonly in nature as sandstone, silica sand or quartzite. It is one of the most abundant oxide materials in the earth's crust. There are three crystalline forms of silica: quartz, tridymite, and cristobalite.

I try to get data on the structure of beta-cristobalite, SiO2. On I find the following:

Cristobalite Downs R T, Palmer D C American Mineralogist 79 (1994) 9-14 The pressure behavior of alpha cristobalite P = room pressure _database_code_amcsd 0001629 4.9717 4.9717 6.9223 90 90 90 P4_12_12 atom x y z B(1,1) B(2,2) B(3,3) B(1,2) B(1,3) B(2,3) Si .30028 .30028 0 .0077 .0077 .00401 -.0003 .0008 -.0008 O .2392 .1044 .1787 .0244 .0086 .0062 -.0013 .0027 .0005

I have no idea what this means. I know the unit cell should have 4 Si atoms, and each should bond to 4 O atoms. What information is given from these numbers (all of them)?

Crystalline silica is a basic component of soil, sand, granite, and many other minerals. Quartz is the most common form of crystalline silica. Cristobalite and tridymite are two other forms of crystalline silica. All three forms may become respirable size particles when workers chip, cut, drill, or grind objects that contain crystalline silica.

Yes. Volcanic ash falls into the air pollutant category of particulate matter. It can cause respiratory and eye symptoms during and after ash fall. The ash contains the minerals quartz, cristobalite, or tridymite. These are free crystalline silica which may cause silicosis which is a disabling and potential fatal lung disease. The recommended respirable exposure limit of 50 ug/m3 of particulate in air can be exceeded for short periods of time.

no

"Silica, also known as silicon dioxide, is a compound made out of the two most abundant elements in the Earth's crust, silicon and oxygen (SiO2). Silica has three main crystalline varieties: quartz (by far the most abundant), tridymite, and cristobalite. Silica is the main constituent of more than 95 percent of rocks that comprise 59 percent of the earth's crust. Quartz makes up about 12 percent of the land surface and about 20 percent of the Earth's crust. The highest levels of silicon in humans are found in the skin and connective tissues. ....."

and silica is the raw material for glass