There are (at least) two ways to import private keys:
- WIF format: https://en.bitcoin.it/wiki/Wallet_import_format
- BIP32: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
WIF it's just the secKey with the checksum, compression flag and nothing else.
BIP32 also contains the derivation info: pubkey, depth, derivation-index, chain-code, parent fingerprint.