Discoasteraceae
Discoaster Tan Sin Hok 1927
Asteroliths exhibit fascinating optical properties. When viewed in the plan view, their stellate or rosette-shaped segments appear in constant extinction (dim) under XPL, with an optic axis vertical relative to the microscope stage. However, when observed from the side, these asteroliths display interference colours due to birefringence. In this orientation, they go dim (extinction position) when their vibration directions align with the polariser and analyser (the extinction angle is 0°). One exception is Discoaster pentaradiatus, which exhibits interference colours even in the plan view. Furthermore, they demonstrate length-slow (+) elongation.
Tan Sin Hok. 1927a. Discoasteridae incertae sedis. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Sect Sci, 30: 411-419.
