How to check if sandisk class 10 is original?

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http://forum.xda-developers.com – Hi, Just got my class 10 64gb xdhc card Paid about 80 usd on it When im testing the card speeds. On my sgs3 im getting 8-10 MB/s read/write transfer rate instead of 30MB/s it suppose to be... My card is ExFAT formatted hard format by pc and im using the external to internal mod How i can verify the authentic of this card? Thanks Sent from my GT-I9300 using xda premium (HowTos)