Rock Preparation for Silicate Hard Rocks

Overview

The working group Petrology / Geochemistry of the Ocean Floor operates a spatially contiguous laboratory complex in building 5 for the exclusive processing of silicate hard rocks. We clean, dry, crush, sieve and pulverize rock samples to determine their major and trace element composition and radiogenic Pb-Sr-Nd-Hf isotope ratios. Since Pb in particular is vulnerable to carryover and contamination, these laboratories were set up to obtain precise measurement results furthermore with the highest possible significance. Since rock processing is a dusty and dirty job, we have a usage concept for all who want to prepare samples here. For further questions, please contact us at rockpreparation(at)geomar.de.

Our Laboratories

When we return from a cruise, the collected samples are not suitable for direct analysis and must be prepared for this. They may be partially weathered or covered with manganese crusts. In addition, igneous rocks contain different minerals with variable distributions. Therefore they have to undergo through a series of physical preparation steps in order to achieve a manageable sample quantity with a representative composition.

[Translate to English:] Gesteinsprobe — Sawn piece of lava (center), sieving fraction (left) and rock powder (right)

Coarse Crushing

Usually, samples arrive in the lab sawn and portioned. If this has not been possible, a water-cooled Norton rock saw is available to remove alteration or manganese crusts, or to cut the rocks into a size suitable for the jaw crusher.

[Translate to English:] Backenbrecher — The Retsch BB 250 jawcrusher is a powerful and modern device with a front door for easy cleaning.

Fine Crushing and Powder Production

Smaller samples, not large enough for the jaw crusher, can be crushed with the Fritsch Pulverisette 13 Disc Mill. The stepless adjustment of the disc spacing produces the required grain size precisely. For the determination of the main and trace element concentrations (by XRF or ICP-MS) of a sample, fine powder is required, which can be produced with the help of a Retsch RM 200 Mortar Mill and a Fritsch Pulverisette 7 Premium Line Planetary Mill. Only agate grinding sets are available.

[Translate to English:] M枚rserm眉hle — Mortar Mill Retsch RM 200 with agate mortar and pistill

[Translate to English:] Scheibenm眉hle — Disc Mill Fritsch Pulverisette 13

[Translate to English:] Planetenm眉hle — Planetary Mill Fritsch Pulverisette 7 Premium Line

Periphery

Some other devices support our work:

Retsch AS 200 Sieving Machine for the production of individual grain size fractions. We have various sieve sets in different sizes and diameters.
Drying cabinets and ultrasonic baths for the time-saving and efficient use of laboratory equipment.

Binoculars and Polarization Microscopes:
An essential aspect of sample preparation is the selection of suitable rock fragments for powder production. For this work, several binoculars and polarizing microscopes are available in the microscopy room. One of the binoculars is equipped with a Leica Flexacam c 3 photo camera and a monitor, so that not only pictures of samples can be taken, but also enable discussions with others on the screen.