From Destinypedia, the Destiny wiki
Location:
Strikes
Rarity class:
Rare
Loot drop:
Yes
Source:
Strikes Public Events High-Value targets
A Concentrated Radiolarian Culture is a Prophecy Offering. It can be obtained from Brother Vance by turning in 10 Radiolarian Cultures with 15 Legendary Shards.
When used as a Prophecy Offering, it charges certain Prophecy Tablets.