Definition

1. Adjective:

   • Shaped like an almond: Having the characteristic oval, tapered form of an almond nut.

2. Noun:

   • A type of volcanic rock: An igneous rock, typically basalt or andesite, containing numerous cavities (amygdules) that have been filled with secondary minerals such as zeolites, calcite, or quartz.

Usage Examples

• Adjective:

  • The amygdaloid structure of the nucleus is visible in the brain scan.
  • The seeds had an amygdaloid form, narrow at one end and rounded at the other.

• Noun:

  • The cliffs were composed of dark, weathered amygdaloid.
  • Geologists study the mineral-filled vesicles in amygdaloid to understand volcanic processes.

Advanced Usage

• In Geology: The term is used specifically to describe the texture of a volcanic rock where vesicles are filled. The rock itself is often referred to simply as "an amygdaloid."
  • The outcrop displayed excellent examples of amygdaloidal basalt.

Variants and Related Words

• Amygdaloidal (adj): The more common adjectival form used to describe the rock texture.

  • The sample had a distinctly amygdaloidal texture.

• Amygdule (n): An individual mineral-filled cavity or vesicle within an amygdaloid rock.

  • Each amygdule in the rock was lined with tiny quartz crystals.

Synonyms

• Almond-shaped (adj): For the adjective form.
• Amygdaloidal basalt (n): A common specific type of this rock.

Notes on Meaning

• The primary, modern use is geological (the noun). The adjectival meaning ("almond-shaped") is technical and less common in everyday language, often found in anatomical contexts (e.g., the amygdaloid nucleus in the brain, named for its shape). The word itself is derived from the Greek , meaning "almond."

Adjective

1. shaped like an almond

Noun

1. volcanic rock in which rounded cavities formed by expanding gas have subsequently become filled with mineral deposits