Printing SecKeyRef reference using NSLog in Objective-C

I am retrieving public key from a certificate with the following code.

- (SecKeyRef) extractPublicKeyFromCertificate: (SecIdentityRef) identity {
    // Get the certificate from the identity.
    SecCertificateRef myReturnedCertificate = NULL;
    OSStatus status = SecIdentityCopyCertificate (identity,
                                              &myReturnedCertificate);

    if (status) {
        NSLog(@"SecIdentityCopyCertificate failed.\n");
        return NULL;
    }

    SecKeyRef publickey;

    SecCertificateCopyPublicKey(myReturnedCertificate, &publickey);
    NSLog(@"%@", publickey);   

    return publickey;
}

I am trying to print the "publickey" variable to see the contents. I am getting runtime error. I would like to know how to print the contents of the "publickey" variable?