gems-inclusions

Two-phase liquid-solid inclusions

A solid phase can be present within fluid inclusion cavity due to two different phenomena:

• Occasional entrapment of a solid particle during crystal growth (captured crystal).
• Precipitation of chemical compounds dissolved in the trapped fluid when it is cooled to the room temperature.

Only in the second case the solid phase can be called “daughter mineral”, because of its formation as a result of precipitation from the trapped fluid. Any phase (solid, liquid, vapor) incorporated in an inclusion during crystal growth and fluid entrapment is called captured phase, in contrast to daughter phases formed from homogeneous fluid once the system (inclusion cavity) was closed.

Tiny crystals of different protogenetic and/or syngenetic minerals can be present in suspension in the fluid during mineralization and hence be trapped together with the fluid inside inclusion cavities. Moreover, particles of such minerals can be deposited on the surface of the growing crystal and act as a barrier for crystal growth, causing formation of fluid inclusion adjacent to solid inclusions. As a result, solid phase can be present inside fluid inclusion cavity too, but it will be captured mineral and not daughter phase.

Daughter minerals are formed be compounds with high solubility; they occur as well formed crystals present in all primary inclusions of the same assemblage (unless necking down took place). They are rather small in comparison with general inclusion volume and the relation of liquid to solid phase volumes is consistent in all inclusions of the same group. Heating of the inclusion will lead to dissolution of daughter minerals, while cooling back will cause their precipitation again, conserving the initial volume of solid phase.

In contrast, captured minerals will be present only in some fluid inclusions of the same group, they tend to have partly dissolved irregular shapes, their volume is very inconsistent, they can be very large with regards to the fluid inclusion volume and in many occasions they will largely overpass the borders of fluid inclusion. Heating of fluid inclusions to the temperature of homogenization of all other phases will not dissolve captured crystals.

 

Captured solid particles (not daughter minerals!) inside liquid-vapor inclusion in emerald from the Urals, Russia.
Field of view 0.15 mm.

 

True primary two phase liquid-solid inclusions are rare because normally a vapor bubble will be also present, forming a typical three phase liquid-solid-vapor inclusion. Such inclusions are characteristic, for example, for Colombian emeralds (see corresponding section).

Nevertheless, some two phase solid-liquid inclusions also can be formed as a result of “necking down” phenomenon, same way as described in the two-phase liquid-liquid inclusion section.

Two-phase water and pyrite (captured) inclusion in quartz from Asturias, Spain. Field of view 8 mm.