Shankha Bhasma is a powder formulation of conch shell. Also in capsule form.
Its usage:

1. It is coolant, improves skin color and complexion.
   
2. It is useful in the treatment of gastritis, abdominal colic, malabsorption syndrome, dyspepsia, vomiting, nausea, acne, etc.
   
3. It is used as ingredient in the preparation of Palash Kshar – Alkali of Butea monosperma.
   Effect on Tridosha – Balances Vata and Pitta.

Dosage:
250 mg – 500 mg once or twice a day before or after food or as directed by Ayurvedic doctor. It is traditionally administered along with honey, lemon juice, Triphala kashaya etc.
Shanka Bhasma preparation, ingredients:
It is prepared from purified Conch shell. There are many different methods of preparation. Any one method can be used. Here is one such method.
Purified Shankha powder is ground with aloe vera juice or lemon juice, made into disc shaped cakes, dried, burnt in absence of air, in 800 – 900 degree celsius, allowed to self cooling. This process is repeated twice to obtain Bhasma.
Reference: Rasa Tarangini.