The word "Dendrachate" is spelled with a "ch" sound rather than a "k" sound due to the origin of the word. "Dendr-" comes from the Greek word "dendron" meaning tree, and "-achate" comes from the Greek word "achates" meaning agate stone. When combined, the "ch" sound is used to mimic the Greek letter chi (χ) which represents a sound similar to "k" and "h" together. Therefore, the IPA phonetic transcription of "Dendrachate" would be /ˈdɛn.drə.keɪt/.
An agate exhibiting in its sections the forms or figures of vegetable growths.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.