School of Engineering and Science - Jacobs University

2. Sample preparation
The majority of this report focuses on geochemical analyses of rock reference
standards issued by governmental or research organizations. However, a brief
description is given of the sample preparation methods used for natural rock samples
that are collected as part of research studies at JUB. Rock samples, whether from
outcrops or drillcores, are first processed by hand-trimming to avoid weathering rinds,
quartz/calcite veining, or obvious alteration features. A geologist’s hammer is used to
produce roughly 50 g of small, 1-3 cm pieces that are crushed in a Fritsch Pulverisette
1 jaw crusher to obtain chips approximately 0.5 cm in size. Harder rock types (e.g.,
chert) are processed more finely to produce smaller sizes (≤0.3 cm chips). Sample
chips are rinsed thoroughly with deionized water to remove dust and dried overnight
in a laboratory oven at ~110 °C, after which approximately 20 g of chips are handpicked
to produce homogeneous samples devoid of secondary mineral veins. The
sample chips are then powdered in a Fritsch Pulverisette 6 planetary mill using agate
balls in a sealed agate mortar.
3. Sample decomposition
The ICPMS used in the JUB Geochemistry Lab is configured to accept
samples in liquid form only, though ICP instruments with laser-ablation attachments
for the analyses of solid samples are increasingly common. One advantage of
converting samples to liquid form is that any effects due to heterogeneities within the
sample (e.g., inclusions or minor mineral phases) are removed, and this approach is
typically termed a ‘whole-rock’ analysis. The common method for rocks and minerals
is to decompose the sample in strong mineral acids at elevated temperatures and
pressures. The decomposition procedures used at JUB, and in fact, many of the
ICPMS techniques as well, have been adapted from methods developed by P. Dulski
at the GeoForschungsZentrum (GFZ) in Potsdam, Germany (see Dulski, 1994;
Dulski, 2001).
Two sample decomposition methods are currently employed: the first is a
high-temperature, high-pressure decomposition utilizing concentrated hydrofluoric
(HF) and perchloric (HClO 4 ) acids that is suitable for the total dissolution of silicatebearing
samples (e.g., iron-formations, basalts), while the second method is a lowtemperature
nitric acid (HNO 3 ) decomposition used for dissolving carbonate samples
such as limestones and dolomites. It is important to note that the HF-HClO 4
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