There is no -cal suffix. There are some words with an -ic suffix and others with -ical. Usually they mean the same thing.
From the OED:
-ic, suffix. Forms: (formerly -ick, ik(e, -ique), primarily forming adjs., many of which are used as ns. The latter have also the form -ics.
Etymologically, the OED comments:
In adjs., immediately representing French -ique, < Latin -ic-us, of Latin origin, as in cīvic-us, classic-us, public-us, domestic-us, aquātic-us, or < Greek -ικ-ός, as in κωμικ-ός cōmic-us, γραμματικ-ός grammatic-us, ποιητικ-ός poētic-us. This was in Greek one of the commonest of suffixes, forming adjs., with the sense ‘after the manner of’, ‘of the nature of’, ‘pertaining to’, ‘of’. Its use in Latin was much more restricted,
A few adjs. in -ic form advs. in -icly, as publicly, franticly,
heroicly; but the adv. is usually in -ically suffix, from the
secondary adj. in -ical suffix.
On -ical, the OED says:
Sometimes forming an adjective from a noun in -ic, as music, musical,
but more frequently a secondary adjective, as comic, comical,
historic, historical. Its origin appears to have been the formation in
late Latin of adjectives in -ālis on nouns in -ic-us, or in -icē...
In French, adjectives of this type are few, and mostly
taken directly from Latin formations, as chirurgical, clérical,
grammatical, médical, etc. But in English they are exceedingly
It elaborates on the -ic/-ical distinction:
Many adjectives have a form both in -ic and -ical, and in such cases that in -ical is usually the earlier and that more used. Often also the form in -ic is restricted to the sense ‘of’ or ‘of the nature of’ the subject in
question, while that in -ical has wider or more transferred senses,
including that of ‘practically connected’ or ‘dealing with’ the
subject. Cf. ‘economic science’, ‘an economical wife’, ‘prophetic
words’, ‘prophetical studies’, ‘a comic song’, ‘a comical incident’,
‘the tragic muse’, ‘his tragical fate’. A historic book is one
mentioned or famous in history, a historical treatise contains or
deals with history.
The conclusion is:
But in many cases this distinction is, from the
nature of the subject, difficult to maintain, or entirely