Which two minerals are known to be cryptocrystalline aggregates besides turquoise?

The correct answer identifies chalcedony and jasper as cryptocrystalline aggregates, which are forms of silica (SiO2) with a microcrystalline structure.

Chalcedony is a type of quartz characterized by its translucent to opaque appearance and is often banded or patterned. Jasper, on the other hand, is a more opaque form of chalcedony that can have rich colors and patterns. Both minerals are composed of very tiny crystals that are not visible to the naked eye, defining them as cryptocrystalline. This specific structure distinguishes them from other forms of quartz that might have larger, visible crystals.

In contrast, the other options include minerals that do not meet the criteria of being cryptocrystalline aggregates. For instance, diamond is a single crystal form of carbon, and opal, while sometimes containing a structure that can appear similar to that of chalcedony, is technically classified as a mineraloid instead of a true crystalline aggregate. Quartz and feldspar are also not cryptocrystalline aggregates; both typically manifest as larger, well-formed crystals. Lastly, ruby and sapphire are both varieties of corundum and exhibit a well-defined crystalline structure rather than a cryptocrystalline one.

Thus, chalcedony and jas