Pearl or parasite enters a bivalve mollusk and settles inside the shell. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate and conchiolin to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Natural pearls come in many shapes, with perfectly round ones being comparatively rare. Typically, the build-up of a natural pearl consists of a brown central zone formed by columnar calcium carbonate (usually calcite, sometimes columnar aragonite) and a yellowish to white outer zone consisting of nacre (tabular aragonite). In a pearl cross-section
Hymn of the Pearl poem. Hymn of the Pearl The Hymn of the Pearl (also Hymn of the Soul, Hymn of the Robe of Glory or Hymn of Judas Thomas the Apostle) is a passage of the apocryphal "Acts of Thomas". In that work, originally written in Syriac, the Apostle Thomas sings the hymn while praying for himself and fellow prisoners. Some scholars believe the hymn antedates the Acts, as it only appears in one Syriac manuscript and one Greek manuscript of the Acts of Thomas. The author of the Hymn is unknown, though there is a belief that it was composed by the