  Magnetization in rock samples is crucial for paleomagnetometry research, as
it harbors valuable geological information on long term processes, such as
tectonic movements and the formation of oceans and continents. Nevertheless,
current techniques are limited in their ability to measure high spatial
resolution and high-sensitivity quantitative vectorial magnetic signatures from
such samples. As a result, our understanding of this magnetization is limited,
specifically for the case of multi-domain samples. In this work we use a newly
developed nitrogen-vacancy magnetic microscope, capable of quantitative
vectorial magnetic imaging with optical resolution. We demonstrate direct
imaging of the vectorial magnetic field of a single, multi-domain dendrite, as
well as the measurement and calculation of the weak magnetic moments of
individual grains on the micron scale. These results pave the way for future
applications in paleomagnetometry, and for the fundamental understanding of
magnetization in multi-domain samples.
