ABSTRACT
References........................................................................................................................................34
It is estimated that the element silicon makes up 27.7% of the earth’s continental crust. The majority
of this silicon is in the form of crystalline silicon dioxide (SiO
) as the polymorph quartz, a well-
established respiratory hazard (Rimala, Greenbergac, and William 2005). However, silicon is also
present in numerous other minerals, and therefore, “silicates and non-silicates” have been used by
mineralogists as a framework, further based on structure (ortho-, ring, chain, sheet, and tecto-), to
describe all minerals (Deer, Howie, and Zussman 1966). This framework has been used in this
chapter, but only minerals that are known or suspected to be respiratory hazards (Guthrie
and Mossman 1993) are included (Figure 2.1 and Table 2.1). The chemistry and structure of
minerals is complicated by the fact that many minerals exist in solid state series and in different
shape “habits.” For example, the chain silicate, amphibole, cummingtonite (Mg,Fe
)
[Si
O
](OH)
-grunerite (Fe
,Mg)
[Si
O
](OH)
series. Grunerite is the name for the more
iron-rich end-members, and is of significance here, because in its fibrous habit it is the mineral
amosite; carcinogenic asbestos (Nolan, Langer, and Wilson 1999). In addition to the chemistry and
habit, the formation conditions of the minerals can have bearings on the toxicity, e.g., SiO
. The
vast majority of crystalline SiO
occurs as the polymorph quartz, a mineral that usually forms at
relatively low temperatures and high pressures. However, if SiO
forms at high temperatures and
low pressures, such as near the surface in a volcanic dome, it forms the SiO
polymorph cristobalite.
Concerns over the possible toxicity of volcanic ash particles have led to research which has shown
that respirable quartz and cristobalite have different bioreactivities in the lung (Housley et al. 2002;
Be
