208 of #365Minerals 🧪⚒️

Astrophyllite:
- A rare silicate mineral
- Forms in alkali granite
- First discovered in 1844
- Its name comes from the Greek words "άστρον/astron" (star) and "φύλλον/phyllon" (leaf) because of its starburst shape #minerals

that preserve their original textures on a sub-micrometer scale. Cathodoluminiscence methods further help to discern whether the rocks have suffered post-depositional alterations or not.

as this ratio can be affected by recrystallisation and later hydrothermal and groundwater alteration. For preventing this the ratio is preferably analysed in interior fossil shell layers belonging to a variety of creatures, from cephalopods to foraminifera,

Burke et al. (1982) did a large study with hundreds of isotopic analyses that showed how this ratio has changed since the Cambrian, allowing to use it as an indirect dating method. Later studies have improved the precision of this curve and further accounted for possible contamination,

as proven by carbonate fossil shells and chemical sediments, whose composition reflects the chemistry of ancient seawater they precipitated from.

with the exception of estuaries and lagoons. This is because Sr has a long residence time in seawater (about 2-2.5 Myr) allowing its mixing by ocean currents. However this ratio has changed through deep time,

👍👍 Muchas gracias, no me esperaba ver a mi carrera y mi máster ahí jaja.

And emeralds weren’t the only chromium-bearing gemstones that formed there, there is also #alexandrite a gem known for its ability to change colour from blueish green to red depending on ambient lighting #afranqueira #gemstonedeposits

It was in such rocks where emeralds formed due to the interchange of elements between the magmas and the surrounding rocks. The presence of high amounts of water in the melts additionally allowed the formation of relatively large crystals.