def properties(lines):
    """Parse properties block

    Returns:
        dict: {property_type: (atom_index, value)}
    """
    results = {}
    for i, line in enumerate(lines):
        type_ = line[3:6]
        if type_ not in ['CHG', 'RAD', 'ISO']:
            continue
        count = int(line[6:9])
        results[type_] = []
        for j in range(count):
            idx = int(line[10 + j * 8:13 + j * 8])
            val = int(line[14 + j * 8:17 + j * 8])
            results[type_].append((idx, val))
    return results
