Needle sensors (pH, H2S, oxygen) have been successfully applied to measure profiles in salt crusts in the Red Sea in Israel (Dr. Don Canfield and Ketil Sørensen, University of Southern Denmark). The researchers drilled a hole to perform the profile measurements, because the crust was impossible to penetrate without breaking the needle sensor.
First, a hole was made in the water-covered gypsum crust with a syringe needle. Then, the equilibrium was allowed to settle in the pore water that filled up the hole. Finally, the profiles were measured with the needle sensors.