A flat slab showing xenocrysts of large green olivine crystals, set in a fine-grained matrix of other minerals. This is an example of the rock where diamonds are found. Specimen is from the Snap Lake diamond mine operated by De Beers Canada Inc. from 2008 to 2015.
Small surveying transits like this were carried into the field to make precision observations and sightings. This E.R. Watts & Sons unit was used by John Anderson-Thomson, an engineer and land surveyor in the NWT for 38 years from 1944 to 1982.