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Yes, "d" is a consonant. It is a voiced dental or alveolar stop sound in English.
It's /z/. In English its place of articulation is alveolar as in the case of /t/, and it is a fricative like /f/.
type 1 alveolar cells
type II alveolar cells
some examples include:
SCRIPTS
SCRIMPS
STRETCH
SHRIMPS
STRINGS
All conform to the 3-1-3 format you described.
Although I only used "S" examples,
consonant combinations in 3s range across:
Hope that helps.