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A few examples:

Crystals & Minerals: Some crystals (like quartz or calcite) naturally form facets that are triangular. Snowflakes often show triangular sub-patterns within their hexagonal symmetry.

Plants: Leaves of certain species (e.g., some begonias, oxalis, and arrowhead plants) are distinctly triangular. The cross-section of some cactus stems also appears triangular.

Animals:
• The dorsal fins of sharks often form triangular silhouettes.
• Many fish tails (caudal fins) are triangular in outline.
• The faces of some insects (like praying mantises) show triangular geometry.
• Bird beaks and reptile heads frequently taper into triangular outlines.

Geological Features:
• Mountain peaks often form triangular profiles (like the Matterhorn).
• Alluvial fans and river deltas sometimes spread in triangular shapes.
• Coastal headlands eroded by waves can leave triangular promontories.

Astronomical & Physical Patterns:
• The Lagrange points in orbital mechanics form triangular arrangements with Earth and the Moon or Sun.
• Certain stress fractures in rocks or mud cracks can create triangular tessellations.
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.Here are some examples of circles in nature:

Planets and Stars – celestial bodies are nearly perfect spheres due to gravity.

Moons and Orbits – many moons are spherical, and orbital paths trace circular or elliptical arcs.

Sun – viewed from Earth, it appears as a circle.

Raindrops – while falling, they form spherical droplets (though not perfect circles when splashing).

Ripples in Water – when an object falls into water, concentric circles spread outward.

Tree Rings – growth rings inside tree trunks form nearly circular layers.

Fruit and Seeds – many fruits (oranges, apples, berries) and seeds (lotus, sunflower centers) have circular cross-sections.

Spider Webs – orb-weaver spiders create webs with circular symmetry.

Animal Markings – spots on leopards, cheetahs, giraffes, and butterflies often take circular shapes.

Eyes – the iris and pupil are circular.

Coral and Jellyfish – corals form circular colonies; jellyfish have round bell shapes.

Hurricanes & Cyclones – storm systems form circular spirals.

Snowflakes (Viewed Microscopically) – while hexagonal, their overall outline is often circular.