  Self-interactions within the dark sector could clump dark matter into heavy
composite states with low number density, leading to a highly suppressed event
rate in existing direct detection experiments. However, the large interaction
cross section between such ultra-heavy dark matter (UHDM) and standard model
matter results in a distinctive and compelling signature: long, straight damage
tracks as they pass through and scatter with matter. In this work, we propose
using geologically old quartz samples as large-exposure detectors for UHDM. We
describe a high-resolution readout method based on electron microscopy,
characterize the most favorable geological samples for this approach, and study
its reach in a simple model of the dark sector. The advantage of this search
strategy is two-fold: the age of geological quartz compensates for the low
number density of UHDMs, and the distinct geometry of the damage track serves
as a high-fidelity background rejection tool.
