Zeolites

The trapps (very thin, fluid lava flows) in India's Deccan region are vast basaltic lava outpourings covering more than 500,000 km2 and accumulating over more than one thousand meters.

Dated at around 65 Ma, they correspond to the end of the Cretaceous and have been linked to the extinction of the dinosaurs. The rise of basaltic lavas is linked to melting zones feeding fractures rather than volcanoes, in connection with the line of "hot spots" (thermally anomalous zones) stretching from Reunion Island to India.

Zeolites develop in cavities formed by gas bubbles trapped in basalt lava flows.

Water slowly alters basaltic glass. The process involves the slow migration and diffusion of ions into the porosity of the lavas during cooling and metamorphism.

Mineral associations are typical of relatively low temperatures and pressure (80-200°C).

Vertical zonation of paragenesis has been observed within basalt layers:

- laumontite is abundant at the base, followed by

- scolécite

and heulandite predominates in the upper part of the flows.

 

In 1756, Swedish mineralogist Axel Frederik Cronstedt discovered the first zeolite, later named stilbite. He recognised zeolites as a new class of minerals, namely hydrated alumino-silicates of alkalis (sodium, potassium, calcium, magnesium).

In India, a dozen zeolites are abundant, including :

Stilbite

NaCa4[Al9Si27O72] - nH2O

Mesolite

Na2Ca2(Al2Si3O10)3·8H2O

Okenite

Ca10Si18O46 - 18H2O

Natrolite

Na2Al2Si3O10 - 2H2O

Apophyllite

KCa4Si8O20(F,OH).8H2O

Heulandite

(Ca, Na)5(Si27Al9)O72 - 26H2O

Laumontite

CaAl2Si4O12 - 4H2O

Zeolites can be synthesised and have numerous industrial applications, such as dehydration (water capture), ion exchange (water softener), thermoregulation (solar energy collector) and pure oxygen extraction for medicine.