Grinding whole spices at home changes a dish more than almost any other equipment decision. A standard American blender is the wrong tool for it, and the reason is geometric.
Blender jars need volume to work
A blender blade creates a vortex that pulls food down into it. That circulation requires enough material, usually with liquid, to keep moving.
A few tablespoons of dry seeds sit below the blade path and get flung to the walls. The machine runs, the spices bounce, and very little grinding happens.
Scaling the batch up to fill the jar fixes the circulation but leaves a cook with far more ground spice than a household will use before it fades.
Grinder cups are sized for the actual task
A dedicated spice or coffee grinder has a small chamber with the blade close to the bottom, so a small load stays in the cutting zone.
The blade also spins considerably faster than a blender's, which matters because dry grinding relies on repeated impact rather than shearing through liquid.
Indian mixer grinders sold in the US usually ship with a dedicated small dry jar for the same reason, alongside larger jars for wet grinding.
Heat is the variable to manage
Grinding generates heat, and heat drives off the volatile aromatic compounds that made grinding worthwhile.
Short bursts with pauses keep the powder cooler than one continuous run, and letting spices cool after toasting before they go in helps as well.
A powder that comes out warm and smells strong in the machine has already lost some of what should have ended up in the food.
What this looks like in a US kitchen
An inexpensive blade coffee grinder kept solely for spices is the common solution, and it handles cumin, coriander, peppercorns and dried chilies well.
Whole spices are stocked by most large supermarkets and by every Indian grocery, usually at a much lower price per ounce in the latter's larger bags.
Cleaning between spices matters more than people expect, since ground residue transfers aggressively. Grinding a spoonful of rice or plain salt and discarding it clears most of the previous load.
The case for the mortar and pestle survives
Crushing rather than pulverizing leaves uneven pieces that release flavor at different rates through cooking, which some dishes are built around.
A heavy mortar also handles wet mixtures of garlic, ginger and salt in quantities too small for any machine to catch.
Neither tool replaces the other, and most Indian kitchens run both because the difference between crushed and ground shows up plainly in the finished dish.