Thank you for submitting your item for appraisal. As you have suggested these could be pieces of graphite, a mixture of graphite and clay that is. They might have been used in an old fashioned thermo-hygrometer recorder. You can check the material with an XRF Spectrometer. Without any definite date or provenance or manufacturer name this would have limited value. Even the Doerner Institute would show no interest. There is no measurement for the sentimental value you might attach to it.