How do I journalize marketable securities with a gain

Example:-

You bought 10 BHP shares for $3,000.

You sold 10 BHP shares for $3,500.

You made a gain of $500 on the 2 transactions.

1) DEBIT Shares Account $3,000
2) CREDIT Bank Account $3,000

Being bought 10 BHP shares for $3,000.

##############################

1) DEBIT Bank Account $3,500
2) CREDIT Shares Account $3,000
3) CREDIT Gain on Shares Account $ 500.

Being sold 10 BHP shares for $3,500
Making a gain of $500.