Jean-Luc Berenguer's blog

Engma 10 resolved : Rocks in powder

Basalt is a volcanic rock (microlitic structure).

From a primary magma from partial melting of the mantle peridotites.

The rocks are classified as basic as base-rich (MgO, FeO) and low alkali (K2O, Na2O).

They are dark because of Fe2O3.






Enigma 10: Rocks in powder !

After the structure, density, porosity, magnetism, mineralogy of rocks, geochemists up!

Enigma 9 resolved : Olivine … what will happen to you ?

The weekly question focused on the difference between the black smokers and white smokers.

All these hydrothermal fields are encountered during oceanographic explorations.

1. Black smokers: they are in the form of chimneys. Emission of sulphurous water at temperatures above 300 º C.

High levels of transition metals. Sulphide deposits in chimneys.

Enigma 9 : Olivine ... what will happen to you?

Olivine is the first mineral to crystallize when magma is cooling.

It is the reason why Olivine is often present in the gabbros, but also in the basalts.

Olivine can crystallize at a temperature of about 1000 ° C. This is the first mineral of the Bowen reaction sequence (see enigma 7: Minerals!)

Enigma 8 resolved : Magnets !

The answer was found by some of our frequent readers. Thank you for following us and explore with us in a fun way, all aspects of geology.

Once the candle lit, the small ring of nickel previously attracted by the magnet will stop being attracted to it and will hang in the vertical piece of wood.

Enigma 8 : Magic magnets

When cores arrive in the lab from the drill floor, scientists and technicians study physical properties of the rocks (magnetism susceptibility for example).
Magmatic rocks contain ferromagnesian minerals (see previous enigma). During the cooling of magma, the rocks, with such minerals can 'fossilized' the magnetic field. Some rocks from the oceanic crust are very amazing.

Enigma 7 resolved : Minerals

The magma produced in the oceanic ridge, while cooling slowly, crystallizes in magmatic rocks.

The challenge for the petrologists on board the JR consists to discover the history of the oceanic crust genesis by the study of minerals in the magmatic rocks.

To resolve the enigma, it is necessary to recall the stages of the minerals crystallization.

Enigma 7 : Minerals

When the magma becomes rock !


Since one month, the scientists aboard the JR have examined with the rocks coming up to the seafloor.

Once their physical properties recorded (see previous enigma), these rocks are described. 

Several teams of researchers and technicians are in charge of this work.



Enigma 6 resolved : Core on deck !

Seven rocks cores from the ocean floor…

among them a sediment core less dense than the others hard rocks cores …

How to find it using the balance only two times ?

A enigma that can be solved as follows (see attached) :

Enigma 6 : Core on deck

Core on deck, core on deck

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