The spelling of /k/ is <k> or <qu>. The /ʒ/ sound is spelled <ge> or <zu>.
The contrast is between a voiceless stop and a voiced fricative, well separated in the mouth. It might be a slight problem for speakers of languages which do not have the /ʒ/ sound, such as German and Arabic.
The /k/ sound can occur in any position in the syllable, but /ʒ/ only occurs finally or intervocalically, other than in foreign names or loan words such as gendarme. /ʒ/ is in any case a very rare phoneme, found in only 334 words in the source dictionary.
The figure for the mean density is too small to be worth calculating. The set makes 3 semantic contrasts, a loading of 75%.
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