Which of the following statements is not true about use of silica in the investment materials?
Silica exists in at least four allotropic forms: quartz, tridymite, cristobalite, and fused quartz. 
When quartz, tridymite, or cristobalite is heated, a change in crystalline form occurs at a transition temperature characteristic of the particular form of silica. For example, when quartz is heated, it inverts (transforms) reversibly from a “low” room-temperature crystal form, known as α quartz, to a “high” form, called β quartz, at a temperature of 573 °C. This α to β phase transformation is called an inversion.
The β-allotropic forms are stable only above the transition temperature noted, and an inversion to the lower α form occurs on cooling in each case.
Ref: Phillip’s 12th edition page 201,202
It acts as refractory
It regulates thermal expansion
Quartz and cristobalite are the allotropic form used in dental investments
Beta allotropic form is stable below transition temperature