The Solana network enforces “rent” for wallet addresses if the rent exemption threshold is not met. In order to support SOL deposits, Gemini enforces a deposit minimum of 0.005 SOL for all SOL deposits. Any deposit of less than 0.005 SOL will not be credited towards your SOL account balance.
This minimum is not applied for SPL tokens.
Note for UK customers:
As of 17th November 2023, only transfers of ERC-20 tokens, ETH, and BTC are supported on Gemini. Whilst you can still freely trade and hold these unsupported tokens within Gemini, we will be removing the unsupported tokens from deposit and withdrawal options, with the exception of transfers to and from a self-hosted wallet. Read more here