The letter ‘K’ is indeed a curious character, as it is like a chameleon, able to change its form and it has a long lineage, including its double life in the Greek, Arabic and Hebrew tongues. Follow this route and you will find its hard sound often assumed by the letter ‘C’ when assimilated into the English language. An example is ‘kabala’ to ‘cabala’.
But the tendency for the ‘C’ to win over the ‘K’ (although both forms may exist between American and British/Australian English) is more evident in words such as ‘ikon/icon’, ‘skeptic/sceptic’, and ‘disk/disc’ where the letter appears within the word. Throw in ‘Q’ for good measure and the chameleon changes again — cite ‘quay/key’ for example.
This chameleon-like nature extends to names where both the ‘C’ and ‘K’ forms co-exist. I’m sure you all know a Catherine and a Katherine.