**Core Concept**
Popcorn calcification is a type of calcification pattern seen on chest X-rays, characterized by small, rounded calcifications that resemble popcorn kernels. This pattern is often associated with certain types of lung tumors, particularly hamartomas.

**Why the Correct Answer is Right**
Hamartomas are benign lung tumors composed of abnormal mixture of epithelial, mesenchymal, and adipose tissue. They are common in middle-aged adults and are often incidentally discovered on chest X-rays. The characteristic "popcorn" calcifications within these tumors are due to the deposition of calcium phosphate crystals within the tumor's fibrotic stroma. This type of calcification is thought to result from the tumor's slow growth and the subsequent fibrosis that occurs as a result of the tumor's degeneration.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because fibrous histiocytoma, a type of skin tumor, typically presents with different radiographic features, such as a well-defined, lobulated mass with a characteristic "dumbbell" shape.
* **Option B:** This option is incorrect because lymphoma, a type of cancer that originates in the immune system, typically presents with a more diffuse or nodular pattern on chest X-ray, rather than the characteristic popcorn calcifications seen in hamartomas.
* **Option C:** This option is incorrect because metastatic disease, such as from a primary lung cancer, typically presents with multiple, bilateral, and often irregularly shaped calcifications.

**Clinical Pearl / High-Yield Fact**
When interpreting chest X-rays, it's essential to remember that popcorn calcifications are a hallmark of hamartomas, and their presence can be used to differentiate these benign tumors from other types of lung lesions.

**Correct Answer:** C. Hamartoma.