"It is a pinnacle of calcium that grows from the floor of limestone cave." This is a description of

Step 1: Analyze the question The question describes a calcium (calcium carbonate) formation that grows upward from the floor of a limestone cave.

Step 2: Explain the concept In limestone (karst) regions, water containing dissolved carbon dioxide (weak carbonic acid) dissolves limestone. When this water drips into a cave, some of it evaporates or loses CO₂, and it leaves behind deposits of calcium carbonate. Two main features form:

• Stalactite: hangs down from the ceiling of the cave, formed by dripping water.
• Stalagmite: builds up from the floor of the cave, formed where the drips land.

Over time, they may meet and form a pillar (column).

Step 3: Check each option

• A. Clint: a block of limestone on the surface of a limestone pavement, separated by grooves called grikes. It is not a cave feature.
• B. Stalagmite: grows upward from the cave floor. ✔
• C. Stalactite: hangs from the cave roof, so it does not match "from the floor."
• D. Stump: not a limestone cave feature (this is a remnant of a tree, or a residual landform in some contexts).

Step 4: Answer The description matches a stalagmite, which is option B.

Memory tip:

• Stalagmite has a g for ground, so it grows from the ground.
• Stalactite has a c for ceiling, so it hangs from the ceiling.