As of Blockstack v0.4.1, the macOS app uses two wallets: the Portal wallet and the Core wallet (This will change in future versions)
Portal Wallet
The Portal wallet is stored in your web browser’s local storage and is used to store the private keys of your identity addresses. These are the addresses that own your Blockstack names.
Write down your Portal wallet backup phrase and keep it somewhere safe to ensure that you can always recover your Blockstack names.
Backup Portal wallet
Step 1: Open Account app
Step 2: Enter password
Step 3: Write down backup phrase
Core Wallet
The Core wallet is the wallet that currently holds your money. When you send Bitcoin to the address displayed in the Wallet app of the Portal, you are actually sending Bitcoin to your Core Wallet. The Core Wallet is stored in the an encrypted, password-protected file in the configuration directory of Blockstack for macOS. Backing up this wallet requires a bit of familiarity with Terminal in the command line.
To start with, you need to look up the password for your Core Wallet. This is generated by Blockstack for macOS the first time you run it and stored in macOS’s secure keychain. You can access by starting the Keychain Access app (search for it in Spotlight if you can’t find it).
Retrieve Core wallet password
Step 1: Open Keychain Access app
Step 2: Search for wallet password entry
Enter blockstack-core-wallet-password in the search field:
Step 3: Display the password
Double-click the blockstack-core-wallet-password entry, click the “Show Password” checkbox and enter your macOS login password to unlock the keychain and display the password.
Next, you should create a backup copy of your Core wallet file.
Create a backup copy of your Core wallet
Step 1: Open Terminal
Step 2: Back up a copy of your Core wallet
The Core wallet that is used with Blockstack for macOS is stored in /Users/<username>/Library/Application Support/Blockstack/config/wallet.json where <username is the username of your macOS account.
For example, my macOS account username is larry so my Core wallet is in /Users/larry/Library/Application Support/Blockstack/config/wallet.json
Copy the wallet file to your desktop so you can copy it somewhere else for safe keeping:
cp "/Users/larry/Library/Application Support/Blockstack/config/wallet.json" ~/Desktop/
With the Core Wallet password and a copy of the wallet.json file you just copied to your Desktop, you can recover any Bitcoin stored in your Core wallet manually should the need arise.