Debian Stretch: SD Card and Micro SD Card on Adapter

To find SD Card:

Way 1:

# df -l
Filesystem     1K-blocks    Used Available Use% Mounted on
...
/dev/mmcblk0p1   1923388  726864   1196524  38% /media/dedetok/AC20-AD23

Way 2:

# parted -l
....
Model: SD 00000 (sd/mmc)
Disk /dev/mmcblk0: 7888MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:
Number  Start   End     Size    Type     File system  Flags
1      1049kB  7888MB  7887MB  primary  fat32        boot, lba

Way 3:

# fdisk -l
...
Disk /dev/mmcblk0: 7.4 GiB, 7888437248 bytes, 15407104 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000
Device         Boot Start      End  Sectors  Size Id Type
/dev/mmcblk0p1 *     2048 15407103 15405056  7.4G  c W95 FAT32 (LBA)

To Format your SD Card

Format SD Card VFAT
1. Umount SD Card
# umount /dev/mmcblk0p1
2. Format SD Card vfat format
# mkfs.vfat /dev/mmcblk0p1

Tested on Debian 9.4 x64