Concept:
Feldspars are important rock-forming minerals. They are alumino-silicates of potassium, sodium, and calcium.
Step 1: Soda feldspar means feldspar containing sodium.
Step 2: The sodium-rich feldspar is known as albite.
Step 3: The chemical formula of albite is:
\[
NaAlSi_3O_8
\]
Step 4: Orthoclase is potassium feldspar, while anorthite is calcium feldspar.
Step 5: Hence, soda feldspar is:
\[
\boxed{\text{Albite}}
\]