Add gallery example for Figure.ternary method

examples/gallery/embellishments/ternary.py

@@ -0,0 +1,35 @@
+"""
+Ternary diagram
+---------------
+
+To plot circles (diameter = 0.1 cm) on a 10-centimeter-wide ternary diagram at the
+positions listed in the sample dataset `rock_compositions`, with default annotations and
+gridline spacings, using the specified labeling.
+"""
+
+import pygmt
+
+fig = pygmt.Figure()
+
+data = pygmt.datasets.load_sample_data(name="rock_compositions")
+
+pygmt.makecpt(cmap="batlow", series=[0, 80, 10])
+
+fig.ternary(
+    data,
+    region=[0, 100, 0, 100, 0, 100],
+    width="10c",
+    style="c0.1c",
+    alabel="Limestone",
+    blabel="Water",
+    clabel="Air",
+    cmap=True,
+    frame=[
+        'aafg+l"Limestone component"+u" %"',
+        'bafg+l"Water component"+u" %"',
+        'cagf+l"Air component"+u" %"',
+        "+givory",
+    ],
+)
+
+fig.show()