Search for fractionally charged particles in lunar soil

A search for stable fractionally charged particles (quarks) in lunar soil was carried out using methods based on the ionic properties which would separate quarks and distinguish them from normal elements. Previous searches in terrestrial substances are reviewed. An upper limit for the concentration in lunar soils, subject to the uncertainties in the physical and chemical properties of quarks, is 2 × ${10}^{-22\mathrm{}}$/nucleon, corresponding to a flux of cosmic-ray origin of less than 5 × ${10}^{-12\mathrm{}}$ ${/\mathrm{c}\mathrm{m}}^2$ sec sr or ${1/\mathrm{m}}^2$ yrsr.