Withdrawals from a Roth IRA are always taken in this order: contributions first, then conversions, then earnings.
Withdrawals on contributions are always tax-free.
Withdrawals of conversions are subject to a 10% penalty if the conversion was less than 5 years ago if you are under age 59-1/2.
Withdrawals of earnings are subject to regular income tax plus a 10% penalty if you are under age 59-1/2.
For example, suppose your IRA contains 10 ounces of gold purchased at $1000 per ounce. Your "contributions" basis is $10,000. You withdraw 6 ounces at $1900 per ounce, the total value being $11,400. That will be taken as a withdrawal of $10,000 of contributions and $1,400 of earnings. Only the earnings are subject to tax and penalty. Then, the remaining contributions basis of your Roth IRA is zero, so all future withdrawals will be withdrawals of earnings. (Unless you make new contributions some time in the future.)
