sound - Can you play Chords on Arduino with a single piezo speaker?

I need to be able to play two tones at once and i have the arduino uni with a small 8ohm piezo speaker. Is it possible to do so?

Sample Code

#define  c     3830    // 261 Hz 

int tone1 = 10; // digital pin10
int tone2 = 9 // digital pin9
void setup() {
    pinMode(tone1, OUTPUT);    // pin as output
    pinMode(tone2, OUTPUT);    // pin as output
} 


void loop() {
   playTone(1000,500,700)
} 

void playTone(long duration, int freq, int freq2) {
    duration *= 1000;
    int period = (1.0 / freq) * 1000000;
    long elapsed_time = 0;
    while (elapsed_time < duration) {
        digitalWrite(tone1,HIGH);

        digitalWrite(tone2,HIGH);
        delayMicroseconds(period / 2);
        digitalWrite(tone1,LOW);
        digitalWrite(tone2,LOW);
        delayMicroseconds(period / 2);
        elapsed_time += (period);
    }
}